Hereditary spherocytosis

INTRODUCTION — Although relatively rare, hereditary spherocytosis (HS) is the most common cause of hemolytic anemia due to a red cell membrane defect. It is a result of heterogeneous alterations in one of five genes that encode red blood cell (RBC) membrane proteins involved in vertical associations that link the membrane cytoskeleton to the lipid bilayer.

The genetics, pathophysiology, clinical features, diagnosis, and treatment of HS will be reviewed here. Other inherited RBC membrane disorders, including hereditary elliptocytosis (HE), hereditary pyropoikilocytosis (HPP), and hereditary stomatocytosis (HSt), are discussed separately, as are general approaches to the evaluation of hemolytic anemia.

●HE and HPP – (See "Hereditary elliptocytosis and related disorders".)

●HSt – (See "Hereditary stomatocytosis (HSt) and hereditary xerocytosis (HX)".)

●Hemolytic anemia, child – (See "Overview of hemolytic anemias in children".)

●Hemolytic anemia, adult – (See "Diagnosis of hemolytic anemia in adults".)

PATHOPHYSIOLOGY — HS is a heterogeneous group of disorders caused by variants in certain genes that encode proteins of the red blood cell (RBC) membrane and cytoskeleton (figure 1); specifically, HS is caused because of inadequate vertical linkages between the cytoskeleton and the lipid bilayer of the RBC membrane (figure 2) [1,2]. The loss of vertical linkages leads to loss of RBC membrane and a spherocytic (rather than biconcave disc) shape of HS RBCs, with decreased surface-to-volume ratio and decreased deformability that is essential to the normal RBC lifespan. (See "Red blood cell membrane: Structure and dynamics".)

Genetics

Overview of the proteins and genes involved — HS is caused by quantitative deficiency of alpha- or beta-spectrin, ankyrin, protein 4.2, or band 3, encoded by the genes SPTA1, SPTB, ANK1, EPB42, and SLC4A1, respectively [2-4]. The studies that have evaluated specific gene variants have generally found that pathogenic variants in these genes tend to be distributed throughout the gene, producing an abundance of variants that are private to individual kindreds rather than localized to specific "hotspots"; this is illustrated in the figure (figure 1) [5-7].

●Spectrin – Erythrocyte spectrin is composed of alpha-beta heterodimers; the proteins are encoded by the SPTA1 and SPTB genes, respectively.

●Ankyrin – Erythrocyte ankyrin is encoded by the ANK1 gene. (See 'Ankyrin deficiency due to ANK1 pathogenic variants' below.)

●Band 3 (the anion exchanger AE1) – This anion channel is encoded by the solute carrier family 4 anion exchanger 1 (SLC4A1) gene. (See 'Band 3 deficiency due to SLC4A1 variants' below.)

●Protein 4.2 (also called band 4.2) – Protein 4.2 is encoded by the EPB42 gene. In the past, protein 4.2 was briefly referred to as pallidin, which is now recognized as a different protein [8,9]. (See 'Band 4.2 deficiency due to EPB42 variants' below.)

●Information from mouse models – The roles of these variants in causing spherocytosis has been studied in several genetically engineered animal models (transgenic mice) and in naturally occurring variants in mice and cattle [10-14]. In the neonatal anemia (Nan) mouse, the variant p.E339D in KLF1, the gene that encodes the erythroid transcription factor Krüppel-like factor 1, results in deficiencies of multiple membrane proteins (alpha spectrin, beta spectrin, ankyrin, band 3, and band 4.1R) and clinical features of HS (spherocytic anemia) [15,16]. The substitution p.E325K in the KLF1 gene, corresponding to the Nan mutation, causes congenital dyserythropoietic anemia (CDA) type IV, with disordered erythropoiesis due to widespread transcriptomic changes affecting many more genes than the ones encoding membrane proteins [17,18].

●Methods of analysis – Quantitative evaluation of the RBC membrane proteins with electrophoresis and immunoblotting, after isolating RBC ghosts with osmotic lysis of RBCs and washing out the hemoglobin and other cytoplasmic proteins, have been used for decades to research and evaluate the protein pathology causing spherocytosis. The discovery of the structural components of the red blood cell cytoskeleton coincided and developed in parallel with the technique of sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) as a tool for protein chemistry in the 1970s [1]. Decrease in a specific protein would be followed up later with sequencing of the corresponding gene, deepening the understanding of erythroid and protein biology along with meticulous work of many research teams around the world.

The introduction of next generation DNA sequencing to clinical diagnostics in approximately 2010 has immensely facilitated diagnosis of RBC and erythropoiesis disorders. Genotype-phenotype correlations associated with HS genes are summarized in the sections below. Additional information about the assembly of these proteins is presented separately. (See "Red blood cell membrane: Structure and dynamics", section on 'Composition of the membrane/cytoskeleton'.)

●Concomitant loss of other membrane proteins – Due to the tight interactions of the RBC cytoskeleton proteins, protein chemistry frequently demonstrates a combination of protein changes. As examples:

•Alpha spectrin deficiency due to SPTA1 pathogenic variants can be associated with concomitant decreases in beta spectrin.

•Ankyrin deficiency due to ANK1 variants is accompanied by secondary spectrin deficiency due to reduced incorporation of spectrin into the membrane since ankyrin is the principal binding site for membrane spectrin [13].

•SLC4A1 variants can also cause secondary band 4.2 deficiency.

•Band 3 loss is a typical finding in all types of spherocytosis regardless of the genetic cause since band 3 is lost along lipid membrane during the development of spherocytes [5].

●Related, non-HS disorders – Variants affecting protein 4.1R, encoded by the EPB41 gene, have not been reported in HS. Protein 4.1R is an integral component of the junctional complex, participating in the horizontal associations of the RBC cytoskeleton; pathogenic variants of this gene cause hereditary elliptocytosis (HE). (See "Hereditary elliptocytosis and related disorders".)

Similarly, pathogenic variants in SPTA1 (encodes alpha spectrin) and SPTB (encodes beta spectrin) that cause qualitative rather than quantitative spectrin abnormalities cause HE rather than HS. Rare pathogenic variants in SPTA1 and SPTB that cause both in spectrin deficiency (a feature of HS) as well as abnormal spectrin tetramer formation (a feature of HE) cause hereditary spherocytic elliptocytosis or pyropoikilocytosis [19-21]. (See "Hereditary elliptocytosis and related disorders".)

Variants affecting the Rh-associated glycoprotein, encoded by the RHAG gene, cause overhydrated hereditary stomatocytosis, while variants in PIEZO1 and KCNN4 cause dehydrated hereditary stomatocytosis or xerocytosis. (See "Hereditary stomatocytosis (HSt) and hereditary xerocytosis (HX)".)

Inheritance patterns — The following inheritance patterns are seen, in some cases related to the specific genes involved:

●HS may be inherited in an autosomal dominant fashion, caused by heterozygous pathogenic variants in ANK1, SLC4A1, or SPTB, seen in approximately 65 to 70 percent of cases [4,6].

●An additional 5 to 15 percent of cases are autosomal recessive, caused by biallelic variants in SPTA1, EPB42, or ANK1 [2,22-25].

●The remaining 15 to 20 percent of cases appear to be due to de novo pathogenic variants [26-31]. Most commonly these occur in the ANK1 gene, likely due to its high G/C content, which predisposes to slipped strand mis-pairing during DNA replication [32].

●A few cases of autosomal recessive HS associated with biallelic ANK1 variants have been described, in which a nonsense variant occurs in trans to a promoter or intronic variant affecting levels of expression, or to a missense variant decreasing but not obliterating the incorporation of ankyrin into the cytoskeleton, leading to a severe, transfusion-dependent disease that remains amenable to treatment with splenectomy [6].

●Very rare cases of autosomal recessive HS due to biallelic SLC4A1 variants have been reported in infants, some requiring in-utero transfusions or born prematurely with life-threatening hydrops fetalis. These infants have severe transfusion-dependent HS, not improving with splenectomy [33,34]. Findings are similar to the most severe form of SPTA1-associated HS due to complete alpha-spectrin deficiency [35]. Biallelic truly null SPTB variants have not been described, indicating that complete beta-spectrin deficiency may be incompatible with life [2].

Ankyrin deficiency due to ANK1 pathogenic variants — Ankyrin is the major protein responsible for the mechanical coupling between the lipid bilayer of the RBC membrane and the underlying spectrin-based cytoskeleton. Ankyrin, along with protein 4.2, anchors the transmembrane protein complexes, composed of band 3 and the Rh-associated glycoprotein (RhAG), to the spectrin tetramers.  

●Over 250 ANK1 pathogenic variants have been described and included in the Human Gene Mutation Database (HGMD) [36,37]. These include missense/nonsense variants, splicing and regulatory substitutions, small and large deletions, insertions, and duplications. Many of these variants are "private" (found in only a single kindred) [38,39].

●ANK1-associated HS is typically an autosomal dominant disease, caused by a monoallelic pathogenic variant, decreasing the expression or incorporation to the cytoskeleton of only up to 50 percent of the ankyrin normally produced. A few cases have been described with biallelic variants, causing recessive, more severe spherocytosis; in those cases (as also discussed above) a null variant is present in trans to a promoter or intronic variant, or a missense variant decreasing but not obliterating expression from that second allele or the amount of protein incorporated in the cytoskeleton. Such combinations lead to a more severe, frequently transfusion-dependent disease, but anemia is still amenable to treatment with splenectomy [6,40].

Patients with a deletion of the short arm of chromosome 8, which contains the ANK1 gene, have been described; these individuals have HS, intellectual disability, and other congenital anomalies [41].

Band 3 deficiency due to SLC4A1 variants — Band 3 has two major functions. It provides cohesion between the RBC plasma membrane and the underlying cytoskeletal proteins, preventing membrane surface loss, and it exchanges bicarbonate for chloride ions, maintaining RBC water content and preventing cellular dehydration.

HS due to SLC4A1 pathogenic variants is typically an autosomal dominant disease presenting as mild hemolytic anemia or even compensated hemolysis. Documented pathogenic variants include missense and nonsense mutations, splicing and regulatory substitutions, small deletions, insertions, or indels, as well as gross deletions and insertions [5,7,37,42-48]. Hemolysis may be aggravated by compound heterozygosity for a pathogenic variant in SLC4A1 in trans to a low-expression band 3 allele [49,50].

Very rare cases of autosomal recessive HS due to biallelic SLC4A1 null variants have been reported in infants requiring in-utero transfusions or born prematurely with life-threatening hydrops fetalis. These infants have severe transfusion-dependent HS, not improving with splenectomy, in addition to severe distal renal tubular acidosis (RTA) [33,34]. (See "Etiology and diagnosis of distal (type 1) and proximal (type 2) renal tubular acidosis".)

Variants in SLC4A1 affecting band 3 can cause other disorders besides HS:

●SAO – A heterozygous deletion of the codons 400 to 408 is the pathogenic variant causing Southeast Asian ovalocytosis (SAO) (picture 1). The molecular change is a deletion of nine amino acids spanning between the cytoplasmic and membrane domain of the band 3 protein causing inactivation of its anion exchanger function, along with a tighter attachment to ankyrin and reduced lateral mobility of the channel, likely underlying the marked rigidity of SAO RBCs [51,52]. Details are discussed separately. (See "Southeast Asian ovalocytosis (SAO)".)

●Distal RTA – Individuals with certain SLC4A1 pathogenic variants causing loss of the anion exchanger function of band 3 can present with an autosomal dominant or autosomal recessive form of distal RTA. Some of these individuals may have HS [43]; however, most of them do not, since glycophorin A (GPA) present in RBCs but not kidney epithelial cells chaperones the distal RTA-causing band 3 molecules to the RBC membrane efficiently [33,43,53-58]. Patients with SAO and distal RTA have been shown to be compound heterozygous for the SAO causing deletion (∆400-408) and a distal RTA-causing variant [59]. (See "Etiology and clinical manifestations of renal tubular acidosis in infants and children", section on 'Genetic causes' and "Etiology and diagnosis of distal (type 1) and proximal (type 2) renal tubular acidosis", section on 'Distal (type 1) RTA'.)

●HS due to protein 4.2 deficiency – The SLC4A1 gene encodes the antigens of the Diego blood group system [60]. Polymorphisms in the gene cause variability of the Diego antigens, which are important for transfusion medicine and neonatal alloimmune hemolytic anemia; however, they are not causing HS or any other RBC pathologies. A notable exception is the common polymorphism c.118G>A (pGlu40Lys), named band 3 Montefiore, which in the homozygous state decreases the incorporation of protein 4.2 into the RBC cytoskeleton by approximately 88 percent, causing HS due to protein 4.2 deficiency [61].

●Cryohydrocytosis – Certain heterozygous SLC4A1 single amino-acid substitutions in the transmembrane domain of RBC band 3 convert its function from an anion exchanger (AE1) into an unregulated cation channel, leaking intracellular K⁺ with a temperature-dependent, passive diffusion process [62]. Such SLC4A1 pathogenic variants cause cryohydrocytosis, a form of hereditary stomatocytosis, where the K⁺ leak decreases at room temperature (23°C) and increases to a maximum when the temperature approaches 5°C [63]. This K⁺ leak via the altered AE1 channel disturbs the osmotic balance and surface-to-volume ratio of the RBCs, leading to chronic hemolysis [64,65].

●Stomatocytosis and dyserythropoiesis – A de novo band 3 variant (p.G796R-band3 CEINGE) was shown to be associated with stomatocytosis and a dyserythropoietic anemia phenotype on bone marrow studies [66].

SLC4A1 pathogenic variants appear to cause approximately 5 percent of HS cases. (See 'Overview of the proteins and genes involved' above.)

However, this may be an underestimate since SLC4A1-associated HS is typically mild and infrequently investigated with clinical sequencing. As mentioned above, band 3 deficiency is a typical phenotypic finding in all types of spherocytosis regardless of the genetic cause since band 3 is lost from the RBC lipid membrane in the process of spherocyte development. (See 'Overview of the proteins and genes involved' above.)

Beta spectrin or alpha-spectrin deficiency due to SPTB or SPTA1 pathogenic variants — beta-spectrin (encoded by SPTB) and alpha-spectrin (encoded by SPTA1) associate in a rod-like heterodimer; two of these heterodimers associate head to head in tetramers that make the sides of each triangular unit in the hexagonal structure of the RBC cytoskeleton.

While spectrin heterotetramers are the main components of the horizontal cytoskeleton, they are also critical for the vertical interactions with the lipid membrane via their binding to ankyrin/band 3 complexes (figure 2). Qualitatively abnormal spectrin causes hereditary elliptocytosis (HE); conversely, quantitative decreases in the amount of spectrin produced or incorporated to the cytoskeleton due to pathogenic variants in the corresponding genes causes HS [2,67]. Abnormalities in both the quality and the quantity of beta-spectrin or alpha-spectrin incorporated into the RBC cytoskeleton cause a mixed phenotype of spherocytic elliptocytosis/pyropoikilocytosis [20,21]. (See "Hereditary elliptocytosis and related disorders", section on 'Hereditary spherocytic elliptocytosis (HSE)'.)

HS due to SPTB pathogenic variants is an autosomal dominant disease that presents as mild to moderate hemolytic anemia. Recessive disease due to truly null biallelic SPTB variants has not been described, indicating that complete deficiency of beta-spectrin is likely to be lethal early in embryonic life. A multitude of pathogenic variants has been described, most of them nonsense mutations, with a few missense mutations, several splicing variants, small deletions, insertions, or indels, as well as gross deletions, insertions, and complex rearrangements [36,48,68-76].

HS due to alpha-spectrin deficiency is an autosomal recessive disease. Each SPTA1 allele produces alpha-spectrin well in excess; therefore, biallelic pathogenic variants are required in SPTA1 to decrease production of the protein enough to cause disease [35,77-81]. The typical genotype for this type of HS is a null SPTA1 variant, such as a nonsense, frameshift, or splicing variant causing nonsense-mediated decay, or whole gene deletion, in trans to the deep intronic variant c.4339-99C>T, also known as alpha-LEPRA (Low Expression PRAgue), which severely decreases the expression of alpha-spectrin from that SPTA1 allele [35,79,80]. This genotype causes severe to moderately severe, most typically transfusion-dependent HS since birth, that nevertheless responds well to splenectomy.

Rare cases of autosomal recessive SPTA1-associated disease with biallelic pathogenic variants causing complete or almost complete alpha-spectrin deficiency may present with fatal hydrops fetalis in the third trimester of pregnancy or with life-threatening anemia in utero if pregnancy is closely monitored. These fetuses can survive to term with in-utero transfusions or if they are delivered prematurely for another reason and receive transfusions in the neonatal period. Characteristic for this disease is reticulocytopenia even when anemic, and the disease does not respond to splenectomy, requiring either lifelong transfusions with chelation therapy or treatment with hematopoietic stem cell transplant (HSCT) [35].

Band 4.2 deficiency due to EPB42 variants — Band 4.2 (also called protein 4.2) strengthens the linkage between band 3 and ankyrin. EPB42-associated HS is an autosomal recessive disease. The typical patient with band 4.2 deficiency is of Japanese ancestry [82]; however, patients of other ethnic backgrounds have also been identified [83,84]. A number of missense and splicing mutations, as well as a few small deletions, indels, and gross deletions, have been reported [85-90]. Other cases of band 4.2 deficiency may be secondary to a variant in SLC4A1 (encoding band 3) that alters its binding with band 4.2 protein and/or its interactions with the cytoskeleton [61,91-94]. As noted above, deficiencies of band 4.2 are rare causes of HS. (See 'Overview of the proteins and genes involved' above.)

Changes in the RBC membrane — Most of the pathogenic variants that cause HS do so by reducing the level of one or more RBC membrane proteins that link the cytoskeleton to the overlying plasma membrane. It is also possible for HS variants to affect protein-protein binding rather than protein abundance. (See 'Overview of the proteins and genes involved' above.)

Studies from animal models suggest that one of the mechanisms of secondary cytoskeletal protein deficiencies involves aberrant sorting of these proteins during the enucleation stage of RBC maturation (when the nucleus is extruded, certain proteins are expelled with the extruded cell nucleus) [95].

The loss of these proteins results in reduced vertical associations between the cytoskeleton and membrane, which in turn cause microvesiculation and progressive membrane loss, the central abnormality that defines HS [96-98]. Loss of membrane reduces the ratio of RBC surface area to volume, in turn creating progressively more spherical cells (picture 2). (See "Red blood cell membrane: Structure and dynamics", section on 'Surface area to volume ratio (SA/V)'.)

There is evidence that membrane loss is present as early as the reticulocyte stage; this distinguishes HS from autoimmune hemolytic anemia (AIHA), in which typically only mature RBCs become spherocytic due to membrane loss [99].

Two hypotheses have been advanced to explain how deficient production or incorporation of these membrane proteins lead to vesiculation and membrane loss. In the first, spectrin deficiency acts directly on the bilayer to create areas of weakness that allow membrane loss. In the second, band 3 deficiency or dispersion causes vesiculation by reducing the integrity of the lipid bilayer [100].

Some individuals with HS have abnormal RBC ion transport, the severity of which may depend on the degree of band 3 (also known as anion exchanger 1 [AE1]) deficiency [101]. On the other hand, all spherocytes demonstrate increased passive permeability to monovalent cations (sodium and potassium) [101,102]. (See "Hereditary stomatocytosis (HSt) and hereditary xerocytosis (HX)", section on 'Control of RBC solute and water content'.)

Mechanisms of hemolysis — Spherocytes are prone to hemolysis. The mechanisms include reduced deformability, which impairs passage through constricted regions of the microcirculation, hemolysis within the splenic microenvironment, and/or phagocytosis by the splenic red pulp macrophages, which may occur in response to splenic trapping [103,104].

Loss of spectrin appears to be especially correlated with the severity of hemolysis [105]; this is seen in the extreme case of severe reticulocytopenia and hemolysis of nascent reticulocytes within the bone marrow in cases of complete alpha-spectrin deficiency [35]. (See 'Beta spectrin or alpha-spectrin deficiency due to SPTB or SPTA1 pathogenic variants' above.)

Once RBCs become spherocytic, successive phagocytosis during repeated passages through the splenic cords (a process termed splenic conditioning) promotes further membrane loss and a progressively more spheroidal shape (picture 2). (See 'Changes in the RBC membrane' above.)

This in turn further impairs passage through the narrow fenestrations of the splenic cords [103,106]. The mechanics of passage through the splenic cords and the effect on spherocytes has been simulated using a two-component RBC model [107]. In severe cases, reduced membrane stability may contribute to mechanical RBC destruction.

In addition to phagocytosis, the spleen also exposes RBCs to an acidotic, oxidizing, metabolically unfavorable environment. RBCs may also become depleted of 2,3-bisphosphoglycerate (2,3-BPG; also called 2,3-diphosphoglycerate [2,3-DPG]), and in certain cases, there may be methylation of membrane proteins (in spectrin deficiency but not in band 3 deficiency) [108].

Case reports have described individuals with the same familial variant who have different severities of hemolysis (variable clinical penetrance). In some cases, this variability has been attributed to concomitant variants in other genes that affect RBC structure and function. As an example, in a family with mild autosomal dominant HS due to partial band 3 deficiency, one family member had more severe clinical features than others, and this was attributed to an exacerbating effect of a variant in PKLR, which encodes pyruvate kinase (PK) [109]. It was speculated that low ATP levels from his partial PK deficiency increased the osmotic fragility of his RBCs. A study from Germany found that PK activity in RBCs from patients with HS were relatively low, particularly in reticulocytes [110]. Loss of membrane-associated PK was proposed to be responsible and might contribute to the severity of HS. Further studies are needed.

As discussed below, splenectomy can virtually eliminate hemolysis and anemia in almost all cases of HS, with the exception of the most severe forms due to complete or almost complete alpha-spectrin or complete band 3 deficiency. The role of splenectomy in HS management is discussed below. (See 'Splenectomy' below.)

EPIDEMIOLOGY

Disease prevalence — HS is seen in all populations but appears to be especially common in people of northern European ancestry. In these individuals, HS affects as many as 1 in 2000 to 1 in 5000 (prevalence, approximately 0.02 to 0.05 percent) [22,23,97,111].

The frequency is thought to be lower in individuals from other parts of the world such as Africa and Southeast Asia, although comprehensive population survey data are unavailable.

In a 2006 study that tested 402 severely jaundiced neonates (requiring phototherapy), four (1 percent) were ultimately diagnosed with HS (ie, approximately 20 times more prevalent than in the general population; approximately one-fifth as prevalent as acquired, immune-mediated spherocytosis) [112]. Other causes of neonatal jaundice and the evaluation of a neonate suspected to have HS are presented below. (See 'Neonates' below and 'Differential diagnosis' below.)

Frequency of different genetic variants — Cohort studies providing relative frequencies of the genes contributing to HS pathogenesis in different populations include:

●In a study of 166 children with HS in Canada, a pathogenic variant was identified in 160 of 166 (97 percent) [48]. The percentages of pathogenic variants were seen:

•ANK1 – 49 percent

•SPTB – 33 percent

•SLC4A1 – 13 percent

•SPTA1 – 5 percent

●In a study of 113 patients with HS from 73 families in India, the variants identified included de novo and dominantly inherited variants in the following genes [68]:

•ANK1 – 53 percent

•SPTB – 36 percent

•SLC4A1 – 4 percent

Compound heterozygous variants in SPTA1 causing autosomal recessive disease were identified in 6 percent.

●In a study of 95 patients in the Netherlands evaluated by next-generation sequencing (NGS) performed in the University Medical Center Utrecht Laboratory, a pathogenic variant was identified in 85 (89 percent) [113].

•SPTA1 – 36 percent, possibly representing a bias of ordering genetic testing in patients with the severe phenotype of SPTA1-associated HS

•ANK1 – 27 percent

•SPTB – 20 percent

●Another study identified autosomal recessive HS due to biallelic pathogenic variants EPB42 in individuals of Japanese ancestry [85,86]. Sporadic cases have also been described in patients of European ancestry [83,84].

CLINICAL PRESENTATION

Disease severity and age of presentation — HS can present at any age and with any severity, with case reports describing a range of presentations from hydrops fetalis in utero through diagnosis in the ninth decade of life [97,100,114-116].

The majority of affected individuals have mild or moderate hemolysis or hemolytic anemia and a known family history, making diagnosis and treatment relatively straightforward [98]. Individuals with significant hemolysis may develop additional complications such as jaundice/hyperbilirubinemia/cholelithiasis (typically exacerbated with concurrent Gilbert syndrome), folate deficiency, or splenomegaly [117].

Hemolytic anemia — A classification for HS has been developed based on the severity of anemia and markers of hemolysis (reticulocyte count and bilirubin) [4,35,86,98,118].

Neonates frequently present with neonatal jaundice that is noted to rise in the first day of life, posing a risk of kernicterus if not monitored and treated appropriately. However, they have a normal hemoglobin at birth. Anemia ensues after two to three weeks as the normal neonatal hyposplenism resolves; hemoglobin frequently decreases enough to require transfusion [2,119].

Transfusion dependence in the first 9 to 12 months of life, when the erythropoietic response may not be adequate, is not necessarily prognostic of the disease severity [120,121]. Infants with an autosomal dominant form of HS based on family history and/or genetic evaluation who require frequent transfusions during the first year of life may benefit from erythropoietin administration [122]. Transfusion dependence beyond the first year of life is not expected for autosomal dominant HS or the autosomal recessive HS due to EPB41 biallelic pathogenic variants, but it is almost always the case for SPTA1-associated autosomal recessive HS. Red blood cell (RBC) indices are described below. (See 'Initial testing' below.)

In older children and adults, the presentation may be that of an incidental finding of hemolysis, hemolytic anemia, or spherocytes on the blood smear (picture 2), or the individual may be symptomatic with anemia, splenomegaly, pigment gallstones, or jaundice. Jaundice due to severe hemolysis is less common after the newborn period, but scleral icterus is not rare, especially when the patient also has Gilbert syndrome [117]. (See 'Older children and adults' below.)

In some cases, co-inheritance of another disorder affecting RBC survival such as sickle cell disease or thalassemia can influence the severity of anemia and make diagnosis more challenging [118]. (See 'Evaluation' below.)

Exacerbations of anemia may also occur in certain settings:

●Infections – Infections that impair erythropoiesis in the bone marrow and thus diminish the capacity to compensate for chronic hemolysis may lead to a period of aplasia. A commonly cited cause of transient aplastic crisis is parvovirus B19 infection; other viral or bacterial infections may also cause transient aplasia. This is because individuals with chronic hemolysis are highly dependent on the accelerated production of new RBCs by the bone marrow, and they can experience a rapid drop in hemoglobin level when the bone marrow is unable to compensate for hemolysis.

In a series of individuals with hereditary hemolytic anemias who presented to the hospital with acute parvovirus infection, common manifestations included fever, musculoskeletal pains, and pancytopenia, while acute kidney injury was also reported, likely due to inadequate supportive management [123]. If an individual with HS develops a precipitous decline in hemoglobin level or reticulocyte count, testing for parvovirus infection is recommended. (See "Clinical manifestations and diagnosis of parvovirus B19 infection".)

Infections may also exacerbate hemolysis, causing worsening of anemia even with increased reticulocyte count and parallel increase of bilirubin and lactate dehydrogenase (LDH). EBV or CMV infection, which typically cause splenomegaly (table 1), may cause increased splenic pooling of RBCs and/or increased hemolysis (hemolytic crisis) in patients with HS or other underlying hereditary hemolytic anemias. (See "Splenomegaly and other splenic disorders in adults", section on 'Splenomegaly'.)

●Nutrient deficiencies – Individuals who become deficient in folate, vitamin B12, or iron may be unable to produce sufficient RBCs to compensate for those destroyed by hemolysis. (See "Clinical manifestations and diagnosis of vitamin B12 and folate deficiency" and "Iron deficiency in infants and children <12 years: Screening, prevention, clinical manifestations, and diagnosis" and "Iron requirements and iron deficiency in adolescents" and "Causes and diagnosis of iron deficiency and iron deficiency anemia in adults".)

●Pregnancy – Anemia may worsen during pregnancy as the RBC mass and plasma volume expand to meet the physiologic needs of the pregnancy. Attention to folic acid supplementation is especially important during pregnancy to avoid increased risk of neural tube defects in the fetus and superimposed megaloblastic anemia for the mother [124,125].

Iron deficiency is rare in hereditary spherocytosis, as in all hereditary hemolytic anemias; therefore, attention must be paid to avoid oral iron supplementation during pregnancy when iron overload may actually be present [124,126]. (See 'Overview of treatment' below.)

Individuals who experience a decline from their baseline hemoglobin level and/or reduction in baseline reticulocyte count are likely to require more frequent monitoring and/or additional testing, details of which will depend on the associated symptoms and laboratory findings.

Complications of hemolysis — Common complications of hemolysis in individuals with HS include neonatal jaundice, splenomegaly, and pigment gallstones, which are discussed in the sections that follow. (See 'Neonatal jaundice' below and 'Splenomegaly' below and 'Pigment gallstones' below.)

Rarely, hemolysis may be severe enough to cause extramedullary hematopoiesis and/or growth delay, along with iron overload due to increased iron absorption and/or transfusions [127,128]. The majority of patients with HS are not thought to be in risk of iron overload [97]; however, there are no extensive studies of older patients, and some cases with iron overload associated with autosomal dominant HS have been reported [129].

Other rare complications that have been reported include leg ulcers, priapism, neuromuscular disorders, cardiac disease, and gout; in some cases, these may represent coincidental rather than causal associations [97,130,131].

Neonatal jaundice — HS may present in the neonatal period with jaundice and hyperbilirubinemia, and the serum bilirubin level may not peak until several days after birth. (See 'Disease severity and age of presentation' above.)

Some experts have proposed that HS is underdiagnosed as a cause of neonatal jaundice [132]. A requirement for phototherapy and/or exchange transfusion during this period is common [97,120]. (See 'Neonates' below.)

Hyperbilirubinemia may be exacerbated by concomitant Gilbert syndrome. (See "Unconjugated hyperbilirubinemia in neonates: Etiology and pathogenesis".)

Splenomegaly — Splenomegaly is rare in neonates but can often be seen in older children and adults with HS [119]. Early reports of family studies found palpable spleens in over three-fourths of affected members, but this may reflect a skewed population with the most severe disease. In these studies, the relationship between disease severity and splenic size was not linear [133].

There is no evidence of an increased risk of splenic rupture.

Indications for splenectomy in HS and possible complications are discussed below. (See 'Splenectomy' below.)

Pigment gallstones — Pigment (bilirubin) gallstones are common in individuals with HS and may be the presenting finding in adults. Gallstones are unlikely before the age of 10 years but are seen in as many as 50 percent of adults, especially those with more severe hemolysis [134]. Gallstones appear to be more common and tend to appear earlier in individuals with Gilbert syndrome (inherited disorder of bilirubin glucuronidation) [117]. (See "Gilbert syndrome", section on 'Long-term complications'.)

Obstructive jaundice or cholecystitis is treated similarly to that in individuals without HS. If cholecystectomy is performed, it may be worthwhile to discuss whether splenectomy was also planned, as the procedures could be combined; however, splenectomy should not be routinely performed during cholecystectomy [118,135-137].

EVALUATION

When to suspect HS — The diagnosis of HS should be suspected in an individual with direct antiglobulin test (DAT; Coombs test)-negative (non-immune) hemolytic anemia and spherocytes on the peripheral blood smear. A positive family history of HS or negative testing for other inherited hemolytic anemias increases suspicion for HS. Severe disease can present in the neonatal period, whereas mild or compensated HS may not present until adulthood. (See 'Disease severity and age of presentation' above.)

Typical findings of hemolytic anemia include low hemoglobin level, high reticulocyte count, high lactate dehydrogenase (LDH) and bilirubin, and low haptoglobin. (See "Diagnosis of hemolytic anemia in adults", section on 'Laboratory confirmation of hemolysis'.)

If hemolysis is severe, the patient may have jaundice (including neonatal jaundice). If compensation is insufficient (if the bone marrow cannot produce new red blood cells [RBCs] with sufficient rapidity to compensate for hemolyzed RBCs), there may be symptoms of anemia. (See "Unconjugated hyperbilirubinemia in neonates: Etiology and pathogenesis", section on 'Increased production'.)

HS is a non-immune form of hemolysis; the DAT is negative. (See "Overview of hemolytic anemias in children", section on 'Intrinsic hemolytic anemias' and "Diagnosis of hemolytic anemia in adults", section on 'Immune versus non-immune'.)

Findings that suggest an alternative diagnosis include prior normal complete blood counts (CBCs) and hemolysis markers. It must be noted that 3 to 11 percent of autoimmune hemolytic anemias may be DAT-negative, depending on the sensitivity of the assay [138,139]. A high-index of suspicion for DAT-negative autoimmune hemolytic anemia (AIHA) must be maintained for a patient presenting with hemolytic anemia with no prior personal and family history, especially with microspherocytes on the smear and other evidence of immune dysregulation [140].

Evaluation of the peripheral blood smear is very helpful; obvious RBC abnormalities may suggest a different type of hemolytic anemia (eg, stomatocytes, ovalocytes, target cells, sickle cells). (See "Evaluation of the peripheral blood smear", section on 'Permutation in shape'.)

Initial testing

All patients — Some aspects of the initial evaluation differ in neonates versus older children and adults since affected neonates tend to have more severe disease and less useful laboratory parameters. (See 'Neonates' below.)

However, the following are appropriate in virtually all individuals:

●CBC and RBC indices – All individuals with suspected HS based on family history, neonatal jaundice, or other findings should have a complete blood count (CBC) with reticulocyte count and RBC indices. The mean corpuscular hemoglobin concentration (MCHC) is often the most useful parameter for assessing spherocytosis; an MCHC ≥36 g/dL is consistent with spherocytes. A normal mean corpuscular volume (MCV) is expected, with a wide (increased) red cell distribution width (RDW); significant reticulocytosis may increase the MCV.

●Blood smear review – All individuals with suspected HS should have a blood smear reviewed by an experienced individual. RBC parameters to be assessed include the presence and abundance of spherocytes, other abnormal RBC shapes, and the degree of polychromatophilia, which reflects reticulocytosis.

●Hemolysis testing – Testing for hemolysis is also appropriate in all patients. This includes lactate dehydrogenase (LDH), indirect bilirubin, haptoglobin, and reticulocyte count. Findings consistent with hemolysis include increased LDH and indirect bilirubin, decreased or absent haptoglobin, and an elevated reticulocyte count.

●Coombs testing – If hemolysis is present, a DAT should be done to evaluate for the possibility of immune-mediated hemolysis, which may be due to hemolytic disease of the fetus and newborn (HDFN) in neonates or autoimmune hemolytic anemia (AIHA) in older children and adults.

The results of testing may also be useful to the transfusion service if transfusion is indicated. The DAT in HS is negative. It should be noted that 3 to 11 percent of AIHAs may also be DAT-negative, depending on the sensitivity of the assay [138,139]. Therefore, a high-index of suspicion for DAT-negative AIHA is indicated for a patient presenting with hemolytic anemia with no prior personal and family history, especially with presence of microspherocytes on the smear and other evidence of immune dysregulation [140].

Our approach to the evaluation is consistent with a 2011 guideline (published in 2012) from the British Committee for Standards in Haematology (BCSH) on the diagnosis of HS and a 2015 guideline from the International Council for Standardization in Haematology (ICSH) on non-immune hereditary RBC membrane disorders [118,141].

Neonates — Neonates with severe hemolysis due to HS may present with neonatal jaundice. (See 'Disease severity and age of presentation' above.)

The evaluation of a neonate with suspected HS depends on whether a parent is known to have HS.

●If an infant with hyperbilirubinemia or other findings of non-immune hemolytic anemia has a known family history of HS, then the likelihood of HS is high, and we rely heavily on the RBC indices. As noted above, an MCHC ≥36 g/dL is highly suggestive of HS. (See 'Clinical presentation' above.)

●If an infant with hyperbilirubinemia or hemolytic anemia does not have a known family history of HS, then a number of other possible diagnoses must be considered. (See 'Differential diagnosis' below.)

Appropriate therapy should not be delayed while determining the underlying cause; likewise, the importance of making the diagnosis of HS should be emphasized regardless of the management interventions needed. Hemolytic anemia with a negative DAT and a high MCHC (eg, ≥36 g/dL) is consistent with HS but must be considered in the context of the entire clinical picture. (See 'Confirmatory tests' below and "Unconjugated hyperbilirubinemia in neonates: Etiology and pathogenesis" and "Unconjugated hyperbilirubinemia in term and late preterm newborns: Screening".)

Neonates with HS tend to have an elevated MCHC (typical range in HS, 35 to 38 g/dL) [119]. This is a useful discriminator between HS and hemolytic disease of the fetus and newborn (HDFN) because HDFN RBCs tend to have MCHC in the range of 33 to 36 g/dL [132].

Spherocytes on the blood smear are helpful if present, but up to one-third of neonates with HS do not have prominent spherocytes, and some neonates without HS have spherocytes [119]. In addition, it may be difficult to assess spherocytes on the peripheral blood smear in a neonate, either because neonates with HS may have fewer spherocytes or because spherocytic cells are often present after birth in neonates without HS [141].

If the infant is well, it is reasonable to postpone testing until approximately six months of age or older, at which time the RBC morphology will be easier to assess [118]. If there is greater urgency to establish a diagnosis (eg, severe anemia or hyperbilirubinemia), specialized testing may be used. (See 'Confirmatory tests' below.)

Older children and adults — As noted above, HS may be suspected in a patient of any age who has evidence of hemolysis (eg, elevated serum LDH, elevated indirect bilirubin, reduced haptoglobin, increased reticulocyte count) or hemolytic anemia that is DAT-negative and not explained by another condition.

HS may also be suspected in an individual who presents with a complication of hemolysis, such as splenomegaly, pigmented gallstones, or an abrupt drop in hemoglobin level when the bone marrow cannot compensate for hemolysis (eg, during a viral illness, pregnancy, or other condition). In such cases, a CBC will be obtained and RBC indices will be available; the reticulocyte count should also be measured if not done already.

Evidence consistent with HS as the likely diagnosis in an older child or adult include the following:

●Positive family history of HS, although this is not always present as some cases arise as de novo pathogenic variants and not all individuals will have a complete family history available.

●Chronic hemolytic anemia, although in mild cases, there may be chronic compensated hemolysis without anemia. The typical reticulocyte count in older children and adults with HS is approximately 5 to 20 percent, but it may be as high as 20 to 30 percent in severe cases.

●Jaundice and/or splenomegaly, although these may be absent if the hemolysis is mild.

●Spherocytes (picture 2) on the peripheral blood smear. The percentage of spherocytes is variable. Pathogenic variants in certain genes have been associated with specific spherocyte morphologies, although the diagnostic value of these findings has not been rigorously tested [5,69,70,142,143] (see 'Genetics' above):

•Anisocytic spherocytes – Ankyrin deficiency

•Pincered or mushroom-shaped spherocytes – Band 3 deficiency

•Acanthocytic spherocytes – Beta spectrin deficiency

•Dense and irregularly shaped cells – Alpha spectrin deficiency

•Ovalocytes and occasional ovalostomatocytes – Protein 4.2 deficiency

●RBC indices consistent with spherocytosis (eg, MCHC >36 g/dL; normal MCV with wide red cell distribution width [RDW]). The MCV and RDW may be increased by greater degrees of reticulocytosis in older children and adults; thus, the MCHC is the most useful of the RBC indices.

The combination of increased MCHC and increased RDW further improves diagnostic performance [144]. If reticulocyte indices are available, a higher-than-average reticulocyte MCHC and a low reticulocyte MCV are also consistent with HS (table 2) [118].

In the appropriate clinical setting, these observations may be sufficient to screen for a diagnosis of HS. (See 'Diagnosis' below.)

In cases that are unclear or if there are questions about the prognosis or if splenectomy is being considered, additional diagnostic confirmation is needed, especially to avoid misdiagnosis of hereditary xerocytosis as HS. The following specialized testing can be pursued. (See 'Confirmatory tests' below.)

Confirmatory tests — A number of tests are available for confirming the diagnosis of HS.

●EMA binding – Eosin-5-maleimide (EMA) binding is a good and widely available test for HS diagnosis; it detects loss mainly of band 3 and Rh-related proteins from the RBC membrane, using EMA, an eosin-based fluorescent dye, that binds to those RBC membrane proteins [145].

The mean fluorescence of EMA-labeled RBCs from individuals with HS is lower than controls, and this reduction in fluorescence can be detected in a flow cytometry-based assay, as illustrated in the figure (figure 3). The reduction in EMA binding is observed in RBCs when HS is due to band 3 deficiency or to deficiencies in other proteins such as ankyrin or spectrin, since the common characteristic in HS is loss of membrane along with band 3 complexes [146]. Two case series of individuals with HS have found the EMA fluorescence in individuals with HS to be approximately two-thirds that of controls [145,147]. Samples can be stored and tested; one of the studies also analyzed the effect of delayed testing and found that samples stored for 24 hours in the darkness gave similar results to those tested immediately [145].

Advantages of EMA binding include its high sensitivity; rapid turnaround time (approximately two hours); and need for only a minimal amount of blood (a few microliters), which is especially advantageous for testing neonates [148-150]. EMA testing can also be used to evaluate for HS-RBCs in a specimen from a patient who has recently received a transfusion [151]. In various studies, the sensitivity and specificity of the test to diagnose HS versus normal RBCs appear to be in the ranges of 93 to 96 and 93 to 99 percent, respectively [148,152-154]. It is important in testing neonatal RBCs to compare the results of EMA binding to control samples from age-matched controls [155].

However, when EMA results for HS are compared with those for other RBC membrane disorders, the specificity of the test declines. EMA binding is also decreased (ie, the test is considered positive) in other hemolytic anemias with loss of membrane associated with band 3 complexes, such as hereditary pyropoikilocytosis, spherocytic elliptocytosis/pyropoikilocytosis, Southeast Asian ovalocytosis (SAO), autoimmune hemolytic anemia, as well as congenital dyserythropoietic anemia (CDA) type II [147,152,156]. False-negative results may be seen in mild cases of HS. (See 'Differential diagnosis' below.)

●Osmotic fragility – Osmotic fragility testing (OFT) is a traditional, specialized test for HS, based on the fact that spherocytic RBCs have reduced surface area to volume (SA/V) ratio. In this test, fresh RBCs are incubated in hypotonic buffered salt solutions of various osmolarities, and the fraction of hemoglobin released (due to hemolysis) is measured. The test takes advantage of the increased sensitivity of spherocytes to hemolysis due to their reduced SA/V ratio (figure 4). Incubation of patient samples for 24 hours prior to testing may accentuate osmotic fragility and improve diagnostic yield.

The OFT has relatively low sensitivity and specificity. It fails to identify a significant number of individuals with HS, and, particularly in the newborn, it may be positive in other conditions including immune hemolytic anemia, hemolytic transfusion reactions, RBC enzyme deficiencies such as glucose-6-phosphate dehydrogenase (G6PD) deficiency, and unstable hemoglobin variants [141]. In one series of 86 individuals with HS, only 57 (66 percent) had positive osmotic fragility testing [157].

●Osmotic gradient ektacytometry – Osmotic gradient ektacytometry (OGE) is the reference method to evaluate RBC membrane disorders [158,159]. It offers accurate (with 100 percent assay sensitivity) diagnosis of HS and excellent specificity in differential diagnosis between the various RBC membrane disorders, including hydration defects   (figure 3) [2,81,156]. The assay evaluates the deformability of RBCs as they are subjected to constant shear stress in a medium of increasing osmolality in a laser diffraction viscometer. The testing has become more accessible over the last decade with the commercial availability of a new generation ektacytometer) [156,160].

Limitations of OGE include its decreased sensitivity after recent transfusions, as with all phenotypic tests that evaluate RBCs as a population. Warm AIHA with a significant number of microspherocytes and CDA-II may produce an ektacytometry curve resembling HS [2,81].

●Glycerol lysis – The glycerol lysis test (GLT) and the acidified GLT (AGLT) are modifications of the OFT that add glycerol (in the GLT) or glycerol plus sodium phosphate (to lower the pH to 6.85, in the AGLT) to the hypotonic buffered salt solutions in which the patient's RBCs are incubated [111,141]. Like EMA, OFT, and OGE, these tests may also be positive in acquired spherocytosis conditions such as AIHA.

The "pink test" is a modification of the GLT in which the final extent of hemolysis is measured in a blood sample incubated in the glycerol solution at pH 6.66 [161]. A further modification has been proposed (the direct pink test) in which the test sample is obtained from fingerprick (or heel puncture in newborns), rather than venipuncture, and incubated directly in the glycerol solution; this requires only a few microliters of blood [162].

●Cryohemolysis – In the cryohemolysis test, RBCs are suspended in a hypertonic solution, briefly heated to 37°C, then cooled to 4°C for 10 minutes [163]. Ease of performance and the wide separation in degree of hemolysis between spherocytes and normal cells are two attractive features of this test [164].

The last two tests (glycerol lysis and cryohemolysis) have limited availability in the United States.

The relative performance of these tests was evaluated in a 2012 study that tested samples from 150 individuals known to have HS [147]. Test sensitivities were as follows:

●AGLT – 95 percent

●EMA binding – 93 percent

●Pink test – 91 percent

●Osmotic fragility, incubated – 81 percent

●Osmotic fragility, fresh – 68 percent

●GLT – 61 percent

Combined testing with EMA binding and AGLT had a sensitivity of 100 percent; combined testing with EMA binding and pink test had a sensitivity of 99 percent; and EMA binding plus osmotic fragility (incubated or fresh) had a sensitivity of 95 percent [147].

Direct comparison of EMA testing versus OGE identified the benefits of EMA testing as a fast, widely available screening test for HS but also indicated the advantage of OGE to differentiate HS from other RBC membrane disorders [156]. When the question is the differentiation between xerocytosis and spherocytosis, before proceeding to splenectomy, OGE as well as genetic evaluation for the pathogenic gene variant is preferable [2,81,156].

These results demonstrate that no single phenotypic testing has 100 percent sensitivity and specificity to accurately identify all individuals with HS, especially if the patient has been recently transfused. Test results should be compared with results of a normal control of similar age, evaluated in parallel with the patient's specimen, as well as with the reference range for many normal samples evaluated by the specific laboratory. Diagnostic yield may be improved by using two tests and by taking into account the personal and family history of the patient and evaluating the blood smear and RBC indices.

These tests can also be positive in other conditions, and the results cannot be interpreted in isolation. If a positive test is not consistent with the clinical picture or findings on the peripheral blood smear, laboratory personnel or a consulting hematologist with expertise in interpreting these tests should be consulted [118].

Specialized testing for selected cases (including genetic testing) — In certain atypical cases in which further characterization of the RBC cytoskeletal/membrane proteins is needed, research-based gel electrophoresis can be done using RBC ghosts.

Clinical grade next generation DNA sequencing is available by several academic and commercial laboratories to evaluate for the genetic cause of an RBC membranopathy or more broadly of a hereditary hemolytic anemia. Identifying a familial disease variant may be useful for prognosis and genetic counseling. (See 'Testing relatives; reproductive testing and counseling' below.)

More importantly, misdiagnosis of hereditary xerocytosis (HX) as spherocytosis has to be avoided, since splenectomy is contraindicated in HX especially, because it predisposes patients to life-threatening venous and arterial thromboembolic complications, and it does not improve hemolysis either [165-167].

Resources for genetic testing are listed on the Genetic Testing Registry website.

Certain academic laboratories have a special interest or ability in performing this testing and may be contacted for further discussions. As examples:

●Cincinnati Children's Molecular Genetics Laboratory:

•Website – www.cincinnatichildrens.org/moleculargenetics

•Phone – (513) 636-4474

●Blood Disease Reference Laboratory Program at Yale University:

•Website – www.medicine.yale.edu/pathology/clinical/mdx/

•Phone – (203) 737-1349

●Mayo Medical Laboratories:

•Website – https://www.mayomedicallaboratories.com/customer-service/contacts.html

•Phone – (800) 533-1710

•Email – [email protected] (United States) or [email protected] (international)

Diagnosis — The diagnosis of HS is made in an individual who presents with DAT-negative hemolysis, an increased MCHC, a positive family history for HS, and/or spherocytes on the peripheral blood smear, by finding a positive result from one or more confirmatory tests such as EMA binding, osmotic fragility, or osmotic gradient ektacytometry (OGE). Specialized testing is especially important if splenectomy is being considered. Specialized testing may be omitted if definitive diagnosis is unlikely to alter management (eg, if hemolysis is mild and childbearing is not planned) or in resource-limited areas of the world [118]. (See 'Confirmatory tests' above.)

For an individual with a strong suspicion of HS and negative or equivocal testing by EMA binding, for whom accurate diagnosis was especially important (eg, due to a previous affected child), positive results from genetic testing are confirmatory for HS. Genetic testing is available in several specialized laboratories. (See 'Specialized testing for selected cases (including genetic testing)' above.)

This testing is similar to that described in published guidelines [118,141]. However, we are more likely to order confirmatory testing in all patients except those in resource-limited settings or those who do not have access to specialized testing for other reasons, as treatment for HS may differ from other conditions (eg, splenectomy is often used in HS but should be avoided in hereditary stomatocytosis). (See 'Splenectomy' below.)

Differential diagnosis — The differential diagnosis of HS includes a number of other hemolytic anemias with spherocytes on the peripheral blood smear:

●Other inherited hemolytic anemias – Other inherited RBC membrane disorders include hereditary elliptocytosis (HE) (picture 3) and elliptocytosis variants (hereditary pyropoikilocytosis [HPP]) (picture 4), overhydrated and dehydrated hereditary stomatocytosis (OHSt and DHSt respectively); DHSt is also known as hereditary xerocytosis (HX) (figure 5). RBC enzyme disorders include glucose-6-phosphate dehydrogenase (G6PD) deficiency, pyruvate kinase (PK) deficiency, and other rarer metabolic disorders.

Like HS, these present with variable degrees of anemia and hemolysis and can be diagnosed at any age. Unlike the other disorders, G6PD deficiency (except for the disease due to rare class I variants) typically presents with episodes of hemolytic crisis after exposure to oxidant drugs rather than chronic hemolysis. Unlike the other membrane disorders, which each have distinctive morphologies on the blood smear, and the enzyme disorders, which typically have nonspecific findings (eg, mild reticulocytosis), HS is characterized by spherocytosis as the predominant morphology. (See "Overview of hemolytic anemias in children", section on 'Intrinsic hemolytic anemias' and "Diagnosis of hemolytic anemia in adults", section on 'Intracorpuscular'.)

It is especially important to distinguish between HS and HSt because HS is generally helped by splenectomy, whereas in HSt, splenectomy should be avoided because it predisposes patients to life-threatening venous and arterial thromboembolic complications, and it does not improve hemolysis either [165-167]. (See 'Decision to pursue splenectomy' below.)

●Neonatal alloimmune hemolytic anemia – Neonatal alloimmune hemolytic anemia, historically known as hemolytic disease of the fetus and newborn (HDFN), is most frequently caused by ABO or Rh incompatibility between fetal RBCs and the mother's immune system; maternal antibodies cross the placenta and recognize the foreign (to the mother) fetal RBC antigens, leading to alloimmune hemolysis. Neonates may present with severe jaundice and anemia requiring aggressive treatment, and like in HS, HDFN can be associated with abundant spherocytes on the blood smear. Unlike HS, HDFN is a transient condition that resolves after the maternal antibodies are cleared, and HDFN is characterized by positive DAT testing, detecting the maternal alloantibodies on fetal RBCs, and demonstrating an immunologically significant discordance between maternal and neonatal blood type. (See "Alloimmune hemolytic disease of the newborn: Postnatal diagnosis and management".)

●Infantile pyknocytosis – Infantile pyknocytosis is a disorder of unknown etiology in which RBCs become hyperdense and dehydrated [168]. Like HS, this condition presents in neonates with anemia and an increased mean corpuscular hemoglobin concentration (MCHC). Unlike HS, the RBCs have irregular borders and varying numbers of projections, and the condition resolves spontaneously during the first year of life (typically, three to nine months after birth) with no other intervention than supportive care (such as treatment of neonatal jaundice with phototherapy and PRBC transfusions as needed).

●Congenital dyserythropoietic anemia (CDA) – CDA type II is an autosomal recessive rare hereditary anemia caused by biallelic SEC23B pathogenic variants. SEC23B encodes a member of the cytoplasmic coat protein II (COPII) complex, which is implicated in intracellular vesicle trafficking in eukaryotic cells, and loss of its function disturbs erythropoiesis. Like HS, some individuals may have significant hemolysis and/or splenomegaly, and like HS, some specialized tests such as EMA binding and OGE may be positive; this is because glycosylation and appropriate positioning of band 3 in the RBC cytoskeleton is compromised [169]. Unlike HS, individuals with CDA-II have the characteristic finding of binucleate and multinucleate erythroblasts in the bone marrow, and the reticulocyte count is typically lower, indicating ineffective erythropoiesis, which in severe phenotypes tend to be associated with significant iron overload, disproportionate to the history of RBC transfusions [118]. (See "Overview of causes of anemia in children due to decreased red blood cell production", section on 'Congenital dyserythropoietic anemia'.)

●Autoimmune hemolytic anemia (AIHA) – AIHA is caused by increased RBC destruction (hemolysis) triggered by autoantibodies directed against self-RBC antigens, with or without complement activation. It is a rare disease with an incidence of 1 to 3 per 100,000 people per year [139]. Warm AIHA associated with an underlying disorder such as systemic lupus erythematosus (SLE) or without an underlying disorder is more common than cold AIHA, which is typically triggered by an infection such as infectious mononucleosis. Like HS, patients can have anemia and/or hemolysis of variable severity and abundant spherocytes on the peripheral blood smear. Unlike HS, in AIHA, DAT is typically positive, the family history is negative for hemolytic anemia, and prior complete blood counts (CBCs) will show a normal hemoglobin level and reticulocyte count. (See "Autoimmune hemolytic anemia (AIHA) in children: Classification, clinical features, and diagnosis" and "Warm autoimmune hemolytic anemia (AIHA) in adults" and "Cold agglutinin disease".)

MANAGEMENT

Overview of treatment — As with most inherited hemolytic anemias, treatment is directed at preventing or minimizing complications of chronic hemolysis and anemia. There are no specific treatments directed at the underlying red blood cell (RBC) membrane abnormality.

Monitoring — The frequency of patient monitoring depends on disease severity and symptoms. (See 'Disease severity and age of presentation' above.)

Babies born to families with history of HS need careful monitoring for hyperbilirubinemia rising already within the first day of life. Anemia ensues typically two to three weeks after birth as the normal neonatal hyposplenism resolves, and hemoglobin frequently decreases enough to require transfusion [2,119].

Once a baseline has been established, an annual visit is sufficient for a child with mild hemolysis, with closer monitoring during viral or other infections that might cause more severe anemia [118]. Growth should be monitored, and patients and/or families should be informed about the possible risk of transient aplastic crisis, including the symptoms and the need to seek medical attention. Adults with mild disease may receive routine medical and preventive care; those with more severe hemolysis may require more frequent monitoring, with the interval depending on their specific needs. (See 'Hemolytic anemia' above.)

Supportive measures — General supportive measures may include the following, depending on disease severity:

●Treatment of hyperbilirubinemia – If a neonate is suspected of having HS (eg, based on positive family history and neonatal jaundice), supportive treatment should be initiated for the neonatal hyperbilirubinemia and/or anemia without awaiting diagnostic confirmation. Therapy for hyperbilirubinemia may range from simple phototherapy to exchange transfusion [119]. (See "Unconjugated hyperbilirubinemia in term and late preterm newborns: Initial management".)

●Folic acid – Folic acid supplementation is appropriate for those with moderate to severe hemolysis and/or during pregnancy. This is based on an increased requirement for folate in RBC production. There are no clinical trials investigating the role of folic acid treatment. However, observational studies that documented megaloblastic anemia in a small number of patients with HS were performed before the institution of routine folic acid supplementation of grains and cereals [98]. This, coupled with the low cost and minimal toxicity of folic acid, make it an attractive and simple therapy to recommend.

The typical dose for infants up to 6 to 12 months of age is 0.4 mg daily, while thereafter 1 mg/day is typically prescribed for those with moderate to severe hemolysis. Individuals with HS of any severity who are planning to be pregnant and during pregnancy should receive a dose of 2 to 4 mg/day. (See "Preconception and prenatal folic acid supplementation".)

For individuals with mild hemolysis who have normal intake of fresh fruits and vegetables (or folic-acid-supplemented grains), daily folic acid is not required, but for those who place a high value on avoiding folate deficiency, which could cause worsening anemia, taking daily folic acid (on the typical dose of 1 mg daily) is safe and inexpensive, and there are essentially no side effects or contraindications.

●Erythropoietin – Erythropoietin (Epo) may be helpful in reducing the need for transfusion in some infants [118,122]. Typically, this can be discontinued around the age of nine months. In one study, the use of recombinant human Epo (1000 international units/kg per week) with iron supplementation obviated the need for transfusion in 13 of 16 infants with HS and severe anemia due to inadequate reticulocytosis during the first months of life [122]. As the infants grew and began to mount an adequate erythropoietic response, the Epo dose could be tapered and discontinued before the age of nine months.

●Considerations related to splenomegaly – There are no special restrictions (eg, no activity limitations) on children with splenomegaly due to HS [118]. However, those with an unusually large spleen should be made aware of the risk of splenic rupture during contact sports. (See "Splenomegaly and other splenic disorders in adults", section on 'Sports participation and fall risk'.)

Transfusions — Blood transfusion is often required in infancy, even in mild autosomal dominant HS. The transfusion requirement in the first months of life does not necessarily predict a severe phenotype. Transfusions may be needed in older children and adults in other settings (eg, aplastic or hemolytic crisis with infections, pregnancy). Typical hemoglobin thresholds for transfusion depend on the age of the patient, symptoms, and comorbidities.

In autosomal dominant HS and in most cases of autosomal recessive EPB42-associated HS, transfusions usually are not required on a chronic basis or for a long enough time to cause iron overload. In contrast, most patients with autosomal recessive SPTA1-associated HS are transfusion-dependent until splenectomy is performed (if appropriate). (See 'Splenectomy' below.)

●Infants – Many infants may require transfusions for anemia, and some may need exchange transfusion for rapidly increasing hyperbilirubinemia. Older children with autosomal dominant HS of mild or moderate severity may tolerate a hemoglobin as low as 7 g/dL without transfusion if reticulocyte count is increasing and this is a temporary anemia exacerbation. However, chronic anemia with Hgb <7 g/dL is typically due to severe autosomal recessive HS caused by SPTA1 (or more rarely ANK1 biallelic variants); inadequate transfusion and chronic anemia in those cases is frequently associated with growth delay and iron overload due to ineffective erythropoiesis. (See "Red blood cell transfusion in infants and children: Indications".)

●Adults – Adults may require transfusions for anemia, with thresholds determined by their clinical status, as discussed in detail separately. (See "Indications and hemoglobin thresholds for RBC transfusion in adults".)

●Aplastic crisis – Individuals with an aplastic crisis due to parvovirus infection or other bone marrow insult may require transfusions if they have a decreasing hemoglobin level without a robust reticulocytosis. The usual course of parvovirus-associated anemia is spontaneous resolution within a few days or weeks. Infected individuals are monitored with twice-weekly complete blood counts (CBCs) and reticulocyte counts to determine the expected hemoglobin nadir and the need for transfusion. (See "Treatment and prevention of parvovirus B19 infection", section on 'Transient aplastic crisis'.)

Consideration of transfusional iron overload typically occurs after transfusion of >15 to 20 units of RBCs (>10 units in smaller children). Adults with mild hemolysis may have a slight increase in iron absorption, and if this occurs in the setting of hereditary hemochromatosis, which is common, iron overload may occur. Screening for iron overload, management, and related subjects are discussed separately. (See "Approach to the patient with suspected iron overload", section on 'Transfusional iron overload'.)

Splenectomy

Decision to pursue splenectomy — Decisions regarding splenectomy must take into account the severity of hemolysis, age of the patient, and the potential perioperative and post-splenectomy long-term complications [118,136,165]. For those with relatively severe hemolysis, splenectomy is effective at improving anemia.

Other considerations include:

●Diagnostic confirmation – It is important to confirm that the diagnosis is HS rather than another inherited hemolytic anemia such as hereditary stomatocytosis (HSt), for which splenectomy is neither safe nor effective. (See 'Differential diagnosis' above and "Hereditary stomatocytosis (HSt) and hereditary xerocytosis (HX)", section on 'Management'.)

●Type of HS (genotype) – Patients with SPTA1-associated autosomal recessive HS with the most common genotype of a null SPTA1 variant in trans to the Low Expression PRAgue (alpha-LEPRA) allele c.4339-99C>T are expected to have transfusion-dependent severe HS that will respond well to splenectomy [35,79,80].

The use of splenectomy in individuals with moderate disease is individualized. We are more likely to advise splenectomy for individuals with more severe hemolysis and/or greater symptoms (eg, abdominal symptoms related to splenomegaly, distress related to jaundice) or for those with growth delays or skeletal changes related to extramedullary hematopoiesis.

In contrast, the most severe cases with HS due to complete alpha-spectrin or band 3 deficiency do not respond to splenectomy, and they require either lifelong chronic transfusions and chelation or hematopoietic stem cell transplantation (HSCT). (See 'Beta spectrin or alpha-spectrin deficiency due to SPTB or SPTA1 pathogenic variants' above.)

For children with HS who remain transfusion-dependent after one year of age, we recommend that genetic diagnosis should be pursued to understand the cause and prognosis and assist with management decisions. Genetic evaluation before planning for splenectomy will also assist to avoid misdiagnosis of hereditary xerocytosis, for which splenectomy will not be safe or effective. (See 'Specialized testing for selected cases (including genetic testing)' above and 'Differential diagnosis' above.)

Autosomal dominant forms of HS generally are not transfusion-dependent after infancy. If the genotype is that of one of the forms of autosomal dominant HS, further evaluation needs to be performed to investigate for comorbidities that would make an autosomal dominant HS present as a transfusion-dependent disease after infancy. (See 'Inheritance patterns' above.)

●Ideal age – Ideally, splenectomy is delayed until the individual is >5 years of age to reduce the likelihood of sepsis due to absent splenic function [118]. It is better to plan for a total splenectomy after the age of five years and after completing the pre-splenectomy immunizations for encapsulated bacteria at that age when the spleen is considered mature enough to mount an optimal response to those immunizations.

Until the age of five years, the patient would likely benefit from a plan for chronic transfusions to avoid growth delay and decrease stress erythropoiesis; monitoring for iron overload and appropriate chelation treatment are used to avoid exacerbation of growth delay by iron overload [170]. (See 'Transfusions' above.)

●Partial versus total splenectomy – In children younger than five years of age for whom chelation is not successful, or if the family/caregivers prefer to avoid chronic transfusions, consideration may be given to partial splenectomy after three years of age. All of the appropriate pre-splenectomy immunizations should be completed prior to partial splenectomy, with the plan to repeat them after five years of age, in case of suboptimal response. A successful partial splenectomy reduces the risk of sepsis from encapsulated bacteria compared to total splenectomy, and in some patients, partial splenectomy may serve as a long-term treatment, even for autosomal recessive HS. (See 'Operative techniques' below and "Elective (diagnostic or therapeutic) splenectomy", section on 'Partial splenectomy'.)

●Gallstone disease – Individuals with symptomatic gallstone disease who require cholecystectomy should be evaluated for the possible role of simultaneous splenectomy, but this should only be pursued if clinically indicated (eg, symptomatic hemolytic anemia and/or severe complications of hemolysis). Simultaneous cholecystectomy can be performed if gallstones are also present. (See 'Pigment gallstones' above and 'Gallstones' below.)

Some individuals with mild hemolysis may pursue splenectomy as a means of reducing gallstone formation, but for most individuals, the risks of splenectomy exceed the possible benefit [171]. (See 'Complications' below.)

●Splenic embolization – In patients for whom splenectomy is appropriate but surgery is refused or contraindicated, partial splenic embolization has been employed, with anecdotal reports of success [172].

Our approach is consistent with a 2011 guideline from the British Committee for Standards in Haematology (BCSH) and a 2017 guideline from the European Hematology Association (EHA) [118,165].

Supporting evidence for splenectomy — There are no randomized trials comparing splenectomy with expectant management. Observational evidence to support the efficacy of both total and partial splenectomy includes the following:

●A 2016 series followed 79 individuals with HS after undergoing partial splenectomy at a single institution in France [173]. The indications for splenectomy were transfusion dependence or severe anemia in 39 and other symptoms (fatigue, gallstones, icterus) in 40. The mean age for splenectomy was 4.3 years for those who were transfusion-dependent and 11 years for those with symptoms of anemia. The procedure involved removal of 85 to 95 percent of splenic tissue using an open approach, with concurrent cholecystectomy if gallstones were present.

At a mean of 11 years of follow-up, all patients but one had a significant improvement in hemoglobin level (mean increase, 0.97 g/dL) and reduction in number of transfusions (from 3.1 to 0.2 per patient per year), a benefit that remained stable or continued to improve over the course of 10 years. A composite endpoint of no symptoms from anemia was documented in 69 of the children (87 percent) and 65 were transfusion-free.

Regrowth of the splenic remnant was common, and 21 patients (27 percent) underwent reoperation with total splenectomy, 49 percent for a significant decrease in hemoglobin and 51 percent for other symptoms related to splenomegaly or hemolysis. The typical interval between the initial partial splenectomy and the subsequent total splenectomy was seven to nine years. Of the 46 who did not undergo concomitant cholecystectomy, 16 (35 percent) developed gallstones, typically several years after splenectomy. There were no severe infections requiring hospitalization and no thrombotic complications.

●Two reports from 2015 and 2016 described outcomes in a consortium registry of patients with a variety of congenital hemolytic anemias (Splenectomy in Congenital Hemolytic Anemia [SICHA]) that included 61 children and adolescents with HS [174,175]. Procedures were evenly divided between total and partial splenectomy; most were performed laparoscopically. Hemoglobin increased in all of the children with HS (mean increase, 4.1 g/dL; greater increases with total than partial splenectomy), and transfusion dependence in the group as a whole decreased from 22 to 4 percent [175].

●A 2001 series of 48 individuals with HS reported that those who had undergone splenectomy had a mean hemoglobin of approximately 15 g/dL, and those who had not undergone splenectomy had a mean hemoglobin of approximately 12 g/dL (table 2) [99].

Additional smaller series have reported similar findings, although some have observed more concerning complications such as post-splenectomy sepsis [176-181]. (See 'Complications' below.)

Pre-splenectomy considerations

Immunizations — For individuals considering splenectomy (total or partial), it is prudent to ensure that all immunizations for encapsulated organisms have been administered with sufficient time to develop an antibody response (typically approximately two weeks before the surgery). Specific recommendations vary based on patient age and number of vaccine doses previously received.

Details of specific vaccines are summarized in the tables for children (table 3) and adults (table 4) and discussed in separate topic reviews. (See "Prevention of infection in patients with impaired splenic function", section on 'Vaccinations' and "Prevention of infection in patients with impaired splenic function", section on 'Children' and "Elective (diagnostic or therapeutic) splenectomy", section on 'Vaccinations'.)

Gallstones — For individuals with gallstones, it may be advantageous to perform simultaneous cholecystectomy at the time of splenectomy. This decision takes into account the size and symptoms of the stones as well as other operative factors. The use of cholecystectomy in individuals with asymptomatic gallstones is controversial; patient values and preferences as well as comorbidities and risks of complications such as cholangitis and acute biliary pancreatitis in a patient with chronic hemolytic anemia and pigment gallstones should be factored into this decision [182]. (See "Approach to the management of gallstones".)

Operative techniques — Splenectomy was traditionally performed as a total splenectomy via laparotomy, which allows a search to be made for accessory splenic tissue, which may be located at other sites within the abdomen. If not removed, an accessory spleen may grow and result in the recurrence of symptomatic anemia [183].

However, laparoscopic splenectomy is increasingly used by surgeons with expertise in this technique. There are no randomized trials comparing open versus laparoscopic splenectomy in HS; however, observational studies in broader pediatric populations and case series have observed that, when performed properly, laparoscopic splenectomy is associated with lower complication rates and shorter hospital stays [184-189]. Laparoscopic splenectomy appears to be equally effective in locating and removing an accessory spleen if present [187]. Thus, laparoscopic splenectomy is used when there is appropriate institutional and surgical expertise [118,190]. In rare cases with a very large spleen, it may be necessary to extend the incision. (See "Elective (diagnostic or therapeutic) splenectomy", section on 'Surgical approach'.)

For younger children who cannot delay splenectomy until after five years of age, we suggest partial splenectomy (also called subtotal or near-total splenectomy). There are no randomized trials comparing partial splenectomy with total splenectomy in HS, and the decision between total and partial splenectomy is made on a case-by-case basis. Compared with total splenectomy, partial splenectomy is likely to be effective in reducing hemolysis while maintaining splenic immune function, although it is probably less effective than total splenectomy in reducing hemolysis [176,177,191-200].

Following partial splenectomy, the spleen eventually regrows and regains part or all of its previous size, and a second (complete) splenectomy may be required. In many cases, this is performed at a time when the patient is considerably older, with a reduced risk of sepsis. Some individuals who undergo near-total splenectomy may have less regrowth of the splenic remnant [194].

Partial/subtotal splenectomy should be accompanied by all of the precautions regarding potential sepsis risk (eg, vaccinations, prophylactic antibiotics for at least a year postoperatively and until residual splenic function can be determined) in case of secondary necrosis of the splenic remnant [191].

Post-splenectomy course — In our experience, the typical post-splenectomy course includes an increase in hemoglobin, a decrease in reticulocyte count, and a decrease in serum bilirubin levels, all of which occur over the course of several days. Often, the hemoglobin and bilirubin become normal or near normal, although RBC survival remains shorter than normal and the reticulocyte count may remain mildly elevated.

In individuals with severe disease due to the common form of SPTA1-associated autosomal recessive HS, the risk of life-threatening anemia and the need for regular transfusions is eliminated, with the hemoglobin reaching normal and sometimes high normal levels with total splenectomy; with partial splenectomy some degree of anemia may persist; adverse effects on growth and development and pain due to splenomegaly will also be ameliorated.

This is consistent with observations published by other experts [118,136,165,201].

The likelihood of requiring cholecystectomy for gallstone disease may also be reduced, as noted above; however, reducing the need for cholecystectomy should not be the sole indication for splenectomy. (See 'Decision to pursue splenectomy' above.)

Patients with the most severe form of HS (near-fatal hydrops fetalis) with complete alpha-spectrin or band 3 deficiency (due to biallelic null variants in SPTA1 or SLC4A1, respectively) do not experience improvement with splenectomy. These patients have required in utero transfusions to reach term delivery, or they were born prematurely and had RBC transfusion support early in the neonatal period. They tend to have a characteristic reticulocytopenia even with significant anemia. These patients can be managed with chronic transfusions and chelation, similarly to thalassemia major patients, or with HSCT [35,81]. (See 'Beta spectrin or alpha-spectrin deficiency due to SPTB or SPTA1 pathogenic variants' above and 'Transfusions' above and 'Hematopoietic stem cell transplantation' below.)

Complications — Splenectomy has a number of known risks of which patients (or parents/caregivers) should be aware [165].

General information about operative and postoperative risks is presented separately. (See "Elective (diagnostic or therapeutic) splenectomy", section on 'Postoperative risks'.)

Evidence regarding postoperative risks specific to HS includes:

●Operative risks – Operative risks such as infection, bleeding, or injury to adjacent organs such as the stomach or tail of the pancreas; these are relatively infrequent.

●Infections – Infections including overwhelming post-splenectomy infection (OPSI), from encapsulated organisms (eg, Streptococcus pneumoniae, Neisseria meningitidis, H. influenzae) that can no longer be removed by normal splenic clearance mechanisms, as well as certain other microorganisms including plasmodia, Babesia, Bordetella, and Capnocytophaga species (from animal bites) [165]. These risks are thought to be highest in the first two to three years following splenectomy and in individuals undergoing splenectomy before five to six years of age, but they also remain elevated for life [202].

•A 1973 review evaluated 850 patients, mostly infants and children, who had undergone splenectomy for HS; 3.5 percent developed sepsis and 2.2 percent died of infection [203].

•A 1995 review evaluated 226 patients with HS who underwent splenectomy up to 45 years earlier [204]. Four deaths from sepsis occurred 2, 18, 23, and 30 years after splenectomy, and the estimated mortality from overwhelming sepsis was 0.73 per 1000 patient-years. The mortality rates for the 35 children who underwent splenectomy prior to six years of age and for the 191 individuals who underwent splenectomy at an older age were 1.12 and 0.66 per 1000 years, respectively, both of which were far higher than those seen in the general population.

•A 1999 review of 264 children who underwent splenectomy at a single medical center reported that 10 (3.8 percent) developed post-splenectomy sepsis within a mean period of two years [205]. Nine of the 10 episodes occurred in patients whose surgery was performed between the ages of zero and five years.

However, risks of sepsis are likely to have declined with improved options for preoperative vaccinations and postoperative prophylactic penicillin. This was illustrated in a 1991 study from the Danish National Patient Registry that demonstrated a dramatic reduction in serious S. pneumoniae infections following pneumococcal vaccination [206]. Individuals who did not receive appropriate pre-splenectomy vaccinations should have a thorough review of their immunization history and should receive vaccinations as discussed separately. (See "Prevention of infection in patients with impaired splenic function".)

●VTE – Venous thromboembolic (VTE) complications include thromboses of the deep veins, pulmonary emboli, splenic or portal vein thrombosis, as well as thrombosis in other unusual sites [207,208]. VTE events appear to be more common in individuals with HS who undergo splenectomy than in those who do not, but the individuals who undergo splenectomy may have had more severe underlying disease, making direct comparisons difficult [137]. Thromboprophylaxis at the time of surgery should be based on standard practices; there is no indication for extended thromboprophylaxis beyond the usual duration [118]. This subject is discussed in detail separately:

•Children – (See "Venous thrombosis and thromboembolism (VTE) in children: Treatment, prevention, and outcome", section on 'Approach to VTE prophylaxis'.)

•Adults – (See "Prevention of venous thromboembolic disease in adult nonorthopedic surgical patients".)

●Arterial thrombosis – Arterial thrombotic events may also be increased relative to individuals with HS who do not undergo splenectomy, with the same caveat that applies to VTE (patients who undergo splenectomy may have more severe underlying disease) [137,209].

●Pulmonary hypertension – It is not clear whether pulmonary artery hypertension (PAH) is a complication of splenectomy in HS. A case report described an individual with HS who underwent splenectomy at the age of 15 years and then developed PAH 32 years later [210]. Retrospective studies have suggested that individuals who have undergone splenectomy for HS and other hemolytic anemias are at greater risk of PAH than those who have not undergone splenectomy; however, it is not clear whether the increased risk is due to the underlying disorder, the splenectomy, or the combination [166,211-214]. In some cases, affected individuals also had hypercoagulable states, potentially further confounding a possible association [212,215]. If PAH occurs, it may take many years. In a study that evaluated 26 children with HS at a median of 4.5 years after splenectomy, none had evidence of PAH [216].

●Frequency of complications – In a 2009 administrative database review spanning the years 1988 to 2004 that included 1657 children and adolescents <18 years with a diagnosis of HS who underwent total splenectomy at an age range of 5 to 12 years, no adverse event occurred in more than 1 percent of the cases during the hospitalization for surgery [217].

Hematopoietic stem cell transplantation — Allogeneic hematopoietic stem cell transplantation (HSCT) is not used in common cases of HS due to an unfavorable risk-benefit ratio; however, a case was reported in which an individual with both HS and chronic myelogenous leukemia (CML) underwent allogeneic HSCT, which cured both disorders [218].

HSCT may be appropriate in the rare cases of autosomal recessive HS due to complete alpha-spectrin or band 3 deficiency, presenting with near-fatal hydrops fetalis, requiring in utero transfusions, or salvaged by premature delivery and early initiation of RBC transfusions; this disease does not respond to splenectomy, and patients require either lifelong chronic transfusions with iron chelation or HSCT [35]. (See 'Beta spectrin or alpha-spectrin deficiency due to SPTB or SPTA1 pathogenic variants' above and 'Transfusions' above.)

Testing relatives; reproductive testing and counseling — If one child is born with HS, there may be concern about HS in a sibling. Thus, if HS is diagnosed in a child, we obtain a full family history and obtain a CBC, reticulocyte count, and examination of the peripheral blood smear on each parent and sibling in order to determine whether the spherocytic gene variant is dominant or recessive.

It is especially important to test a newborn sibling for HS, as well as newborns of affected parents for HS (testing that may require additional confirmatory testing such as EMA binding, osmotic gradient ektacytometry, or targeted sequencing for a known familial variant causing HS), as this may be associated with severe degrees of hyperbilirubinemia and anemia during the neonatal period. (See 'Confirmatory tests' above.)

Appropriate counseling can be performed once this information has been obtained. This may be done by a clinician with expertise in hemolytic anemias or by a genetic counselor. It is possible for an individual with no hemolysis, no spherocytes on the blood smear, and a normal reticulocyte count to be a carrier of HS, which may be relevant in certain kindreds [118]. (See "Genetic counseling: Family history interpretation and risk assessment".)

For individuals of childbearing age with HS, review of the familial gene variant and its mode of transmission (autosomal dominant or recessive) may be useful for informing discussions of the likelihood of HS in children. If the familial variant is known to act in an autosomal dominant fashion, it is important to make this information clear in the prenatal record and to make the information available to the pediatrician before delivery in order to stress the importance of close monitoring for neonatal hyperbilirubinemia starting at the first day of life [119]. Some individuals who had HS as a child and were treated with splenectomy may have forgotten about the condition or may not realize the implications for their child.

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Anemia in adults".)

SUMMARY AND RECOMMENDATIONS

●Genetics and pathophysiology – Hereditary spherocytosis (HS) is a heterogeneous group of disorders caused by variants in certain genes that encode proteins of the red blood cell (RBC) membrane skeleton:

•Spectrin (SPTA1 and SPTB genes)

•Ankyrin (ANK1 gene)

•Band 3 (SLC4A1 gene)

•Protein 4.2 (EPB42 gene)

These abnormalities decrease the levels of proteins that link the RBC inner membrane skeleton to the outer lipid bilayer (figure 2), which in turn leads to membrane vesiculation, spherocyte formation, and hemolysis. Approximately three-fourths of these variants show autosomal dominant inheritance, 10 to 15 percent show autosomal recessive inheritance, and the remainder are de novo variants, most frequently of ANK1, causing new autosomal dominant disease. (See 'Pathophysiology' above.)

●Prevalence – HS is seen in all populations but appears to be especially common in people of northern European ancestry, where it affects up to 1 in 2000 to 1 in 5000 (prevalence 0.02 to 0.05 percent). HS may account for as many as 1 percent of infants with neonatal jaundice. (See 'Epidemiology' above.)

●Clinical findings – HS can present at any age and with any severity. The majority of affected individuals have mild or moderate hemolytic anemia. Neonates with HS often have jaundice and hyperbilirubinemia; the serum bilirubin level may not peak until several days after birth, but it may increase rapidly, even on the first day of life. In older children and adults, HS may present as an incidental finding of hemolytic anemia or spherocytes on the blood smear (picture 2), or the individual may be symptomatic from anemia, splenomegaly, or pigment gallstones. Exacerbations of anemia may occur with parvovirus infection, mononucleosis, or pregnancy. (See 'Clinical presentation' above.)

●Evaluation – All individuals with suspected HS based on a known family history and/or clinical findings should have complete blood count (CBC) with reticulocyte count, evaluation of RBC indices, review of the blood smear by an experienced individual, testing for hemolysis, and direct antiglobulin testing (DAT; Coombs testing). In neonates or infants, a mean corpuscular hemoglobin concentration (MCHC) ≥36 g/dL is highly suggestive of HS. Spherocytes and reticulocytosis are less reliable indicators in infants but are important in older children and adults. (See 'Initial testing' above.)

●Diagnostic confirmation – Several tests are available to confirm the diagnosis of HS (see 'Diagnosis' above):

•OF – Osmotic fragility is the traditional confirmatory test. (See 'Confirmatory tests' above.)

•EMA – EMA (eosin-5-maleimide) binding is a widely available and sensitive test requiring as little as 5 microL of blood. (See 'Confirmatory tests' above.)

•Ektacytometry – Osmotic gradient ektacytometry is very sensitive and the most specific phenotypic test, especially in differentiating HS from other RBC membrane disorders; it requires at least 0.3 mL of blood. (See 'Confirmatory tests' above.)

•NGS – Next generation DNA sequencing (NGS) is helpful if the patient has been transfused and phenotypic testing of their RBCs is compromised with donor RBCs. Sequencing panels for RBC membrane disorders or hereditary hemolytic anemias are often used. NGS is also useful when deciding whether to pursue splenectomy and making other treatment decisions. (See 'Specialized testing for selected cases (including genetic testing)' above.)

●Differential diagnosis – The differential diagnosis of HS includes other hemolytic anemias with spherocytes on the blood smear (figure 5). Other inherited RBC membrane disorders include hereditary elliptocytosis (HE), hereditary stomatocytosis or xerocytosis syndromes (HSt or HX), and congenital dyserythropoietic anemia (CDA) type II. Other possible diagnoses in neonates include neonatal alloimmune hemolytic anemia and infantile pyknocytosis. Other possible diagnoses in children and adults include autoimmune or drug-induced hemolytic anemias. (See 'Differential diagnosis' above.)

●Management – Treatment of HS is directed at minimizing complications of chronic hemolysis and anemia. (See 'Management' above.)

•Monitoring and supportive care – Close monitoring is important for neonates, who may require phototherapy for hyperbilirubinemia, and, in severe cases, exchange transfusion. Even neonates with mild autosomal dominant HS may develop anemia severe enough to require RBC transfusion two to three weeks after birth. If the transfusion requirement persists after two to three months of age in these infants, erythropoietin may be used to reduce transfusion requirements. For those with moderate to severe hemolysis, we suggest folic acid supplementation (Grade 2C); a typical dose is 1 mg/day. Higher folic acid doses are required during pregnancy, as presented separately. (See 'Overview of treatment' above and "Preconception and prenatal folic acid supplementation".)

•Transfusions – Blood transfusion is often required in infancy, even in mild autosomal dominant HS. The transfusion requirement in the first months of life does not necessarily predict a severe phenotype. Transfusions may be needed in older children and adults in other settings (eg, aplastic or hemolytic crisis with infections, pregnancy). Typical hemoglobin thresholds for transfusion depend on the age of the patient, symptoms, and comorbidities. Transfusional iron overload may occur after transfusion of >15 to 20 units of RBCs (>10 units in smaller children), and appropriate monitoring is required, with chelation indicated in some cases. (See 'Transfusions' above.)

•Splenectomy – For children with HS whose disease remains transfusion-dependent or who are severely symptomatic from anemia >1 year of age because of SPTA1-associated autosomal recessive HS, we recommend a chronic transfusion program with chelation until they are at least three years of age. Partial splenectomy can be considered at that age (provided there is adequate surgical expertise) (Grade 2C). We suggest postponing total splenectomy until >5 years of age, after the appropriate pre-splenectomy immunizations are completed, to reduce the risk of sepsis. (Grade 2C). Some families with children >5 years old may elect to have a total splenectomy rather than partial splenectomy as the initial procedure. Observational data demonstrate a dramatic reduction in transfusion requirements after splenectomy. The use of splenectomy in individuals with moderate disease, typically autosomal dominant HS, is individualized based on symptoms (discomfort from splenomegaly, distress from jaundice). In those cases, partial splenectomy (provided there is adequate surgical expertise) may offer a better balance of benefits versus long-term risks. (See 'Decision to pursue splenectomy' above.)

•Pre-splenectomy considerations and splenectomy risks – For individuals considering splenectomy, all immunizations for encapsulated organisms should be administered with sufficient time to develop an antibody response. For individuals with gallstones, it may be possible to perform simultaneous cholecystectomy at the time of splenectomy. Patients should be aware of different operative techniques (partial versus total splenectomy; open versus laparoscopic procedures) and potential complications, which include potentially life-threatening sepsis, venous thromboembolism (VTE), and possibly arterial thromboembolic events or pulmonary hypertension. It is important to confirm that the patient does not have HSt, for which splenectomy is contraindicated since it is neither safe nor effective in limiting hemolysis. (See 'Pre-splenectomy considerations' above and 'Operative techniques' above and 'Complications' above and "Elective (diagnostic or therapeutic) splenectomy", section on 'Postoperative risks'.)

•Relatives – Testing relatives, reproductive testing, and/or genetic counseling may be useful. (See 'Testing relatives; reproductive testing and counseling' above.)

ACKNOWLEDGMENT — UpToDate gratefully acknowledges Stanley L Schrier, MD (deceased), who contributed as Section Editor on earlier versions of this topic and was a founding Editor-in-Chief for UpToDate in Hematology.