Version July 2025
| Condition | β-globin genotype | Neonatal screening* | By age 6 weeks¶ | Older children (≥5 years), adolescents, and adults | ||||
| Hb A (%) | Hb A2 (%)Δ | Hb F (%)◊ | Hb S (%) | Hb C (%) | ||||
| No hemoglobinopathy | ββ | FA | FA or AF | 95 to 98 | 2 to 3 | <2 | 0 | 0 |
| Beta thalassemia trait | β/β0 or β/β+ | FA | FA | 90 to 95 | >3.5 (unless due to δβ-thalassemia; can be normal or lower) | 1 to 3 (significantly higher if due to δβ-thalassemia) | 0 | 0 |
| Sickle cell trait | ββS | FAS§ (or FSA§) | FAS | 50 to 60 | <3.5 | <2 | 35 to 45; may be lower if concomitant alpha thalassemia | 0 |
| Homozygous sickle anemia (Hb SS) | βSβS | FS | FS | 0 | <3.5 but may be increased with concomitant α-thalassemia. May be falsely elevated when measured by HPLC. | 5 to 15; may be higher in rare cases or with hydroxyurea therapy | 85 to 95 | 0 |
| Sickle-β0 thalassemia | βSβ0 | FS | FS | 0 | >3.5 but may be falsely elevated when measured by HPLC | 2 to 15 | 80 to 92 | 0 |
| Sickle-β+ thalassemia | βSβ+ | FSA or FS¥ (or FAS§) | FSA | 3 to 30 | >3.5 but may be falsely elevated when measured by HPLC | 2 to 10 | 65 to 90 | 0 |
| Hb SC disease | βSβC | FSC | FSC | 0 | <3.5 | 1 to 5; may be higher in rare cases | 45 to 50 | 45 to 50 |
| Hb CC disease‡ | βCβC | FC | FC | 0 | <3.5 | <2 | 0 | 95 |
| Hb C trait‡ | ββC | FAC (or FCA§) | FAC | 50 to 60 | <3.5 | <2 | 0 | 40 to 50 |
δβ: delta-beta; DNA: deoxyribonucleic acid; Hb: hemoglobin; Hb A: adult hemoglobin; Hb F: fetal hemoglobin; HPLC: high-performance liquid chromatography.
* The neonatal screening patterns list the different hemoglobins in order of abundance. As an example, the FAS pattern has the greatest amount of Hb F, followed by Hb A, followed by Hb S. These are the common or typical patterns. Note that there may be differences due to laboratory reporting rules, prematurity, age of testing, biological variation, and transfusion. The more common exceptions are noted in the table. Newborn screening is a screening test that should not stand alone, and a diagnostic test is always needed to confirm abnormal findings.
¶ In term infants. The transition to adult Hbs may be delayed with prematurity (consideration of post-conceptual age may be necessary).
Δ Hb A2 levels can also be influenced (decreased) by δ-thalassemia mutations, which are not exceedingly rare and are clinically silent beyond the effect on Hb A2 levels. Iron deficiency can also decrease Hb A2 levels.
◊ Hb F levels may be higher as a hereditary trait (eg, non-deletion hereditary persistence of fetal hemoglobin [HPFH]). Common non-deletion HPFH determinants can be co-inherited with any hemoglobinopathy.
§ At birth, the abundance of all adult Hb species (eg, Hb A, Hb S, Hb C) is very low relative to Hb F. The small amounts of the adult Hb species may be challenging to accurately quantify relative to each other. Depending on laboratory methods and reporting rules, some newborns with sickle cell trait may have an FSA pattern (instead of the typical FAS pattern). Similarly, some newborns with sickle-β+ thalassemia may have an FAS pattern (instead of the typical FSA pattern). A similar discrepancy can occur with Hb C trait and Hb C-β+ thalassemia. Newborn screening is a screening test that should not stand alone, and a diagnostic test is always needed to confirm abnormal findings.
¥ In sickle-β+ thalassemia, the quantity of Hb A at birth may be insufficient for detection. Hb A will become quantifiable during the first few months of life.
‡ In Hb C trait, concomitant alpha thalassemia variants lower the percentage of Hb C, and Hb C levels <40% after iron deficiency is excluded or corrected may indicate a two-gene deletion at the alpha locus. Hb C trait plus a beta thalassemia variant could be misdiagnosed as Hb CC disease.
Adapted from: Sickle cell disease in children and adolescents: Diagnosis, guidelines for comprehensive care, and care paths and protocols for management of acute and chronic complications. Revised at the Annual Meeting of the Sickle Cell Disease Care Consortium, Sedona, AZ, November 10-12, 2001.
With additional data from: Bain BJ. Sickle cell haemoglobin and its interactions with other variant haemoglobins and with thalassaemias. In: Haemoglobinopathy Diagnosis, 2nd ed, Wiley-Blackwell, Oxford, 2005.
