INTRODUCTION —
The most common presentations of venous thrombosis are deep vein thrombosis (DVT) of the lower extremity and pulmonary embolism (PE). The causes of venous thrombosis can be inherited or acquired and are often multiple in a given patient.
The causes and risk factors for venous thrombosis will be reviewed here (table 1) [1,2]. The diagnostic approach to DVT and PE, the evaluation for risk factors in patients with documented venous thrombosis, and etiologies of upper extremity venous thrombosis are discussed separately.
●(See "Primary (spontaneous) upper extremity deep vein thrombosis".)
●(See "Catheter-related upper extremity venous thrombosis in adults".)
VIRCHOW'S TRIAD AND RISK FACTOR PREVALENCE —
Identifying risk factors raises clinical suspicion for thrombosis and may influence treatment.
Virchow's triad — Virchow's triad is the underlying pathophysiology of thrombosis formation [3] and includes the following:
●Blood flow stasis
●Vascular endothelial injury
●Hypercoagulable state
Risk factor prevalence in VTE — A risk factor (table 1) can be identified in >80 percent of patients with venous thromboembolism (VTE). Furthermore, more than one factor is often present in a given patient. As examples:
●Many patients with an episode of VTE have more than one acquired risk factor for thrombosis [4-6]. In one study, over one-third of patients had one to two risk factors and 53 percent had three or more risk factors [4]. In another study, the combination of a major medical illness plus immobilization increased the risk of VTE 11-fold [6].
●Patients may also have combinations of both inherited and acquired thrombophilic defects, driving up the overall risk of thrombosis (table 2). One-half of thrombotic events in patients with inherited thrombophilia are associated with the additional presence of an acquired risk factor (eg, surgery) [7].
●Some patients with VTE have more than one type of inherited thrombophilia, which leads to a significant increase in the risk of developing VTE. This has been shown in the general population in individuals who are heterozygous for both the factor V Leiden and prothrombin G20210A mutations [8]. (See 'Common inherited hypercoagulable states' below.)
ACQUIRED RISK FACTORS —
There are many acquired risk factors for thrombosis (table 1). Common risk factors include prior thromboembolism, active malignancy (including myeloproliferative neoplasms [MPNs]), recent major surgery, trauma, immobilization, heart failure, older age (≥65 years), pregnancy, inflammatory bowel disease (IBD), exogenous estrogens, and antiphospholipid antibodies (aPL) (table 1).
Previous thromboembolism — Previous venous thromboembolism (VTE) is a risk factor for recurrence. The risk is cumulative and dependent upon patient-specific factors. Assessing this risk, which can range from low to high, is discussed separately. (See "Selecting adult patients with lower extremity deep venous thrombosis and pulmonary embolism for indefinite anticoagulation", section on 'Assessing risk of recurrence'.)
The site of the first VTE appears to predict future sites of recurrence. Patients presenting with pulmonary embolism (PE) are more likely to recur with PE than deep vein thrombosis (DVT) [9,10]. Similarly, patients who present with DVT are more likely to recur with DVT, although DVT often occurs in the contralateral leg [11].
Active malignancy — VTE occurs in approximately 15 percent of patients with active malignancy, especially those with advanced disease at the time of diagnosis (eg, pancreatic cancer) and those with MPNs. The risk is increased further by major surgery, chemotherapy, hospitalization, and the presence of intravenous catheters (eg, peripherally inserted central catheters [PICCs], port-a-cath, Hickman line). Studies have reported unprovoked VTE can precede the diagnosis of malignancy in older individuals [12-14], but this is less commonly seen in the era of age-appropriate cancer screening [15]. This risk is discussed in detail separately. (See "Cancer-associated hypercoagulable state: Causes and mechanisms" and "Multiple myeloma: Prevention of venous thromboembolism" and "Cancer-associated hypercoagulable state: Causes and mechanisms", section on 'Therapy-related factors' and "Evaluating adult patients with established venous thromboembolism for acquired and inherited risk factors", section on 'Evaluation for occult malignancy'.)
The impact of hyperviscosity in myeloproliferative syndromes is discussed below. (See 'Hematologic conditions' below.)
Surgery — Thrombotic risk increases during surgery, particularly orthopedic and major vascular, pelvic, neuro-, and cancer surgery [16-19]. The risk of thrombosis in nonorthopedic and orthopedic surgery is discussed separately.
Trauma — The risk of thrombosis is increased in all forms of major injury, especially spinal cord injury [20-23], and possibly in mild trauma, especially if an inherited thrombophilia is present (eg, trauma not requiring surgery, a plaster cast, hospitalization, or extended bed rest at home for at least four days) [24]. VTE risk in trauma patients is discussed separately. (See "Venous thromboembolism risk and prevention in the severely injured trauma patient", section on 'Pathophysiology and risk factors'.)
Immobilization (including hospitalization) — Venous stasis associated with bed rest, hospitalization, or prolonged immobilization (eg, intensive care unit admission, heart failure, stroke, myocardial infarction, leg injury) is an important risk factor for venous thrombosis [25,26]. VTE following stroke, hospitalization, and lower extremity injury are discussed separately. (See "Prevention and treatment of venous thromboembolism in patients with acute stroke" and "Prevention of venous thromboembolic disease in acutely ill hospitalized medical adults", section on 'Epidemiology' and "Prevention of venous thromboembolism (VTE) in adults with non-major extremity orthopedic injury with or without surgical repair", section on 'Risk of thrombosis'.)
Prolonged travel, especially by air, appears to confer a small increase in VTE risk (termed the "economy class syndrome"). This subject, including possible preventive measures, is discussed in detail separately. (See "Pathogenesis, risk factors, and prevention of venous thromboembolism in adult travelers", section on 'Epidemiology' and "Pathogenesis, risk factors, and prevention of venous thromboembolism in adult travelers", section on 'Risk factors'.)
Older age (≥65 years) — Data supporting age as a risk factor for DVT include the following:
●One observational study reported that the annual incidence of DVT increased from 17 per 100,000 persons/year for those between the ages of 40 and 49 to 232 per 100,000 persons/year for those between the ages of 70 and 79 [27].
●Another study reported an increasing incidence of VTE with age (hazard ratio [HR] 1.7 for every decade of life after 55 years) [28].
Pregnancy — The risk of thrombosis during pregnancy is approximately four times higher than in nonpregnant female patients. This subject is discussed in depth separately. (See "Venous thromboembolism in pregnancy: Epidemiology, pathogenesis, and risk factors", section on 'Epidemiology'.)
The risk of thrombosis is further accentuated when inherited thrombophilia is present. Details regarding inherited thrombophilias and VTE risk in pregnancy are described separately. (See "Inherited thrombophilias in pregnancy" and "Venous thromboembolism in pregnancy: Prevention".)
Chronic inflammatory bowel (and liver) disease — Despite an elevated international normalized ratio, patients with chronic liver disease are at increased risk of VTE. Further details are provided separately. (See "Hemostatic abnormalities in patients with liver disease".)
VTE is a known complication of IBD (ie, Crohn disease, ulcerative colitis). This subject is discussed further separately. (See "Clinical manifestations, diagnosis, and prognosis of ulcerative colitis in adults", section on 'Extraintestinal manifestations' and "Clinical manifestations, diagnosis, and prognosis of Crohn disease in adults".)
Cardiovascular
Heart failure — Heart failure is a hypercoagulable state [29] that can result in intracardiac thrombus and DVT. The risk of DVT may be greatest in patients with right heart failure (eg, those with peripheral edema) and those who are hospitalized for heart failure (adjusted HR 3.13) [30].
Established atherosclerotic heart disease — Patients with established atherosclerotic heart disease are at increased risk of VTE [31-33]. For example, an observational study reported that myocardial infarction or stroke was associated with a fourfold increased risk of VTE within three months of the event [31]. Another study suggested that those at greatest risk were older, Black, and female patients [33].
Conversely, patients with DVT may be at increased risk of atherosclerotic disease [34-39]. In one cohort study, patients with VTE had a twofold risk of having asymptomatic atherosclerotic disease compared with those who did not have VTE [32]. In other studies, patients with VTE had a 1.5- to threefold risk of an acute myocardial infarction or stroke [34,37].
Cardiovascular risk factors — Patients with risk factors for cardiovascular disease are also at risk for VTE [28,40], especially age (see 'Older age (≥65 years)' above), obesity, and smoking:
●Obesity – Several studies have found an increased risk for VTE (two- to threefold) and VTE recurrence in patients with obesity [28,41-44] and a reduced risk for underweight patients [45]. In one study, the greatest impact was seen in those below the age of 40 [44].
Obesity further increases the risk of VTE when patients have factor V Leiden or the prothrombin gene mutation, undergo extended travel, or are taking hormonal contraceptives [43,46,47]
●Smoking – Most studies report a relationship between smoking and VTE risk with relative risks ranging from 1.3 to 3.3 [48-50]. In one meta-analysis of 32 observational studies, compared with "never smokers," the relative risk (RR) of VTE was 1.17 ("ever smokers"), 1.23 (current smokers), and 1.1 (former smokers). The risk increased by 10 percent for every additional ten cigarettes smoked per day or by 6.1 percent for every additional ten pack-years [50]. Additional risk factors, such as obesity or contraceptive use, increased the risk further [50,51].
●Others – Other factors that may be associated with an increased risk of VTE include male sex, diabetes, and possibly hypertension and hypercholesterolemia [41,52,53].
In a cohort study of 40,000 female patients, those who were nonsmokers were physically active, and consumed alcohol in moderation were at a lower risk of developing VTE [54].
Drugs — Several drugs have been associated with an increased risk of venous thrombosis. Statin use may be associated with a reduced risk of recurrence after a first episode of VTE [55].
Hormonal — Several hormonal therapies are associated with an increased risk of VTE:
●Contraceptives – Oral and transdermal contraceptive use (which contain estrogen) is a cause of thrombosis in young female patients [56-59].
The risk of thrombosis increases within the first 6 to 12 months of therapy [60] and is unaffected by duration of use. The risk likely returns to previous levels within one to three months of cessation [59].
Whether there is an additive risk with contraceptives and nonsteroidal anti-inflammatory agents is unclear [61].
Further information on VTE risk and contraceptives are provided separately. (See "Combined estrogen-progestin contraception: Side effects and health concerns", section on 'Venous thromboembolism' and "Contraception: Transdermal contraceptive patches", section on 'Risk of venous thrombotic events' and "Transgender women: Evaluation and management", section on 'Estrogen therapy'.)
●Hormone replacement therapy – Data support an increased risk of VTE in female patients who take oral, but not transdermal, estrogen as part of menopausal hormone therapy. This subject is discussed in detail separately. (See "Menopausal hormone therapy: Benefits and risks", section on 'Venous thromboembolism'.)
●Testosterone – It is controversial as to whether there is an increased risk of VTE in some individuals taking testosterone, most commonly in those who develop erythrocytosis. However, a systematic review and meta-analysis did not find a statistically significant association between VTE and testosterone [62]. (See "Testosterone treatment of male hypogonadism", section on 'Venous thromboembolism'.)
●Tamoxifen – Tamoxifen is associated with an increased risk of VTE, especially when additional risk factors are present (eg, surgery, cancer, fracture). (See "Managing the side effects of tamoxifen and aromatase inhibitors", section on 'Venous thromboembolism'.)
Cancer therapy — Several chemotherapeutic agents (eg, cisplatin, asparaginase), immunomodulatory agents (eg, thalidomide, lenalidomide), antiangiogenic drugs (eg, bevacizumab), and cyclin-dependent kinase inhibitors used to treat cancer have been associated with an increased risk of thrombosis. The use of erythropoiesis-stimulating drugs has also been shown to increase the risk of thrombosis in cancer patients receiving chemotherapy. (See "Cancer-associated hypercoagulable state: Causes and mechanisms".)
Antiphospholipid antibodies — Patients with aPL are at risk of developing venous or arterial thrombosis. They are given the diagnosis of antiphospholipid syndrome (APS) when they develop thrombosis or recurrent fetal loss. The risk of thrombosis in those with aPL and APS manifestations are discussed separately. (See "Clinical manifestations of antiphospholipid syndrome", section on 'Thrombotic events'.)
Kidney diseases — Patients with end-stage kidney disease, nephrotic syndrome, and kidney transplant are at increased risk for VTE [63-67]. Data supporting this risk include the following:
●One study reported a higher annual frequency of PE in adults with end-stage kidney disease and chronic kidney disease compared with those who had normal kidney function (527, 204, and 66 per 100,000 persons, respectively) [68].
●Other observational data reported a relative VTE risk of 1.7 for patients with stage 3/4 chronic kidney disease compared with patients with nonimpaired kidney function [66].
●Patients with the nephrotic syndrome have an increased prevalence of both arterial thromboembolism and VTE (10 to 40 percent), particularly DVT and renal vein thrombosis. These data are discussed separately. (See "Hypercoagulability in nephrotic syndrome", section on 'Pathogenesis' and "Hypercoagulability in nephrotic syndrome", section on 'Epidemiology' and "Venous thrombosis and thromboembolism (VTE) in children: Risk factors, clinical manifestations, and diagnosis", section on 'Other venous thrombosis'.)
●The prevalence of VTE following kidney transplantation is in the range of 5 to 8 percent, with PE being a common cause of death [69,70]. In one study of 484 kidney transplantation patients, 7 percent developed VTE at a median time of 6.5 months post-kidney transplantation (range 1 to 81 months) and 50 percent had recurrence following cessation of oral anticoagulants [69].
Risk factors for VTE in stages 1 to 3 chronic kidney disease include albuminuria (urinary albumin ≥30 mg/24 hours) and a low estimated glomerular filtration rate (<75 mL/minute per 1.73 m2) [71,72].
The reason for the increased risk is unknown but may relate to elevated levels of factor VIII and Von Willebrand factor in this population [73].
Hematologic conditions
●Heparin-induced thrombocytopenia – Venous and arterial thrombosis is the major clinical problem associated with heparin-induced thrombocytopenia (HIT). The risk of thrombosis in HIT is described separately. (See "Clinical presentation and diagnosis of heparin-induced thrombocytopenia", section on 'Incidence and risk factors'.)
Very rarely, patients can develop a HIT-like syndrome in the absence of heparin exposure, referred to as autoimmune HIT or spontaneous HIT. Coronavirus disease 2019 (COVID-19) virus-induced immune thrombotic thrombocytopenia is one such syndrome. (See "Virus-induced immune thrombotic thrombocytopenia (VITT) and VITT-like disorders".)
●Hyperviscosity – Thrombosis is a complication of hyperviscosity (ie, increased plasma viscosity, number of red or white blood cells, or decreased cell deformability).
•Hyperfibrinogenemia and hypergammaglobulinemia – Increased plasma viscosity can result from hyperfibrinogenemia or hypergammaglobulinemia. Hyperviscosity-associated hypergammaglobulinemia is most commonly encountered in Waldenstrom macroglobulinemia or multiple myeloma. (See "Epidemiology, pathogenesis, clinical manifestations, and diagnosis of Waldenström macroglobulinemia", section on 'Hyperviscosity syndrome' and "Multiple myeloma: Prevention of venous thromboembolism", section on 'VTE incidence and risk factors' and "Disorders of fibrinogen".)
•Myeloproliferative neoplasms (MPNs) – Increased whole blood viscosity (and platelet defects) play an important role in the pathogenesis of thrombosis in polycythemia vera. Common thrombotic complications include cerebrovascular accidents, myocardial infarction, peripheral arterial occlusion, DVT, PE, and portal and hepatic vein thrombosis (Budd-Chiari syndrome).
Essential thrombocythemia is also associated with an increased risk of thrombotic complications, particularly in association with the presence of the JAK2 V617F mutation; it can also lead to hemorrhagic complications when the platelet count is very elevated.
A high percentage of patients with idiopathic hepatic vein thrombosis (eg, Budd-Chiari syndrome) or portal vein thrombosis, but not those with idiopathic lower extremity DVT [74-77], have evidence of an occult MPN (lack of an elevated hematocrit or platelet count in association with the presence of the JAK2 V617F, CALR, or MPL mutations) [78-81]. (See "Etiology of the Budd-Chiari syndrome", section on 'Myeloproliferative disorders' and "Clinical manifestations and diagnosis of polycythemia vera", section on 'Thrombosis and hemorrhage' and "Essential thrombocythemia: Clinical manifestations and diagnosis", section on 'Thrombosis and hemorrhage'.)
•Hyperleukocytosis and leukostasis – Increased whole blood viscosity also occurs in occasional patients with myeloid and monocytic leukemias who have markedly elevated white blood cell counts (generally >100,000/microL). Small vessels in the lungs, brain, and (less commonly) other organs can be obstructed by high levels of immature leukocytes. (See "Hyperleukocytosis and leukostasis in hematologic malignancies".)
•Sickle cell disease – Increased whole blood viscosity in sickle cell disease is primarily due to decreased deformability of sickled erythrocytes and may contribute to the occlusion of small blood vessels. Other factors that may play a role in this complication include enhanced adhesion of sickle erythrocytes to vascular endothelium and increased coagulation and platelet activation [82-84]. (See "Overview of the clinical manifestations of sickle cell disease", section on 'Venous thromboembolism' and "Overview of the pulmonary complications of sickle cell disease", section on 'Venous thromboembolism and pulmonary thrombosis'.)
●Paroxysmal nocturnal hemoglobinuria (PNH) – PNH is a rare acquired clonal disorder of bone marrow stem cells. Approximately 40 percent of patients develop thrombosis, typically in the intraabdominal venous network (mesenteric, hepatic, portal, splenic, and renal veins) and cerebral vessels as opposed to a lower extremity or lung [85]. (See "Clinical manifestations and diagnosis of paroxysmal nocturnal hemoglobinuria", section on 'Thrombosis'.)
Miscellaneous — Several other conditions are associated with an increased risk of VTE [45,86-109], most of which are discussed separately:
●Hyperhomocysteinemia – (See "Overview of homocysteine".)
●Polycystic ovary syndrome – (See "Clinical manifestations of polycystic ovary syndrome in adults", section on 'Venous thromboembolism'.)
●Ovarian hyperstimulation syndrome – (See "Pathogenesis, clinical manifestations, and diagnosis of ovarian hyperstimulation syndrome", section on 'Specific complications'.)
●Central venous lines and PICCs – (See "Central venous catheters: Overview of complications and prevention in adults" and "Central venous catheters: Overview of complications and prevention in adults", section on 'Catheter malfunction'.)
●Superficial vein thrombosis – (See "Superficial vein thrombosis and phlebitis of the lower extremity veins".)
●COVID-19 and COVID-19 vaccination – (See "COVID-19: Hypercoagulability" and "Virus-induced immune thrombotic thrombocytopenia (VITT) and VITT-like disorders" and "COVID-19: Vaccines".)
●Rheumatoid arthritis – (See "Overview of pleuropulmonary diseases associated with rheumatoid arthritis", section on 'Venous thromboembolic disease'.)
●Active tuberculosis – (See "Pulmonary tuberculosis disease in adults: Clinical manifestations and complications", section on 'Venous thromboembolism'.)
●Sepsis – (See "Prevention of venous thromboembolic disease in acutely ill hospitalized medical adults", section on 'Intensive care unit patients'.)
●Klinefelter syndrome – (See "Clinical features, diagnosis, and management of Klinefelter syndrome", section on 'Comorbidities'.)
●Chronic psoriasis – (See "Psoriasis: Epidemiology, clinical manifestations, and diagnosis".)
●Obstructive sleep apnea – (See "Clinical presentation and diagnosis of obstructive sleep apnea in adults", section on 'Complications'.)
●Antineutrophil cytoplasmic antibodies-associated vasculitis – (See "Granulomatosis with polyangiitis and microscopic polyangiitis: Respiratory tract involvement".)
●Microalbuminuria – (See "Moderately increased albuminuria (microalbuminuria) and cardiovascular disease".)
●Anemia (in acutely ill hospitalized patients) – (See "Diagnostic approach to anemia in adults".)
●Sarcoidosis – (See "Sarcoidosis-associated pulmonary hypertension: Diagnostic evaluation in adults", section on 'Pulmonary vascular disease'.)
●Hereditary angioedema – (See "Hereditary angioedema (due to C1 inhibitor deficiency): Epidemiology, clinical manifestations, exacerbating factors, and prognosis".)
●Intravenous drug use
●Asthma (the contribution of glucocorticoid use is unknown)
●Vacuoles, E1 enzyme, X-linked, autoinflammatory, somatic (VEXAS) syndrome – VEXAS syndrome, due to somatic mutations in UBA1, is a rare acquired autoinflammatory disorder with systemic manifestations including thrombosis. In one observational study of 119 patients with VEXAS syndrome, almost one-half had thrombosis, 80 percent of which was venous (cumulatively 40 percent at 5 years) and the remainder arterial (cumulatively 11 percent at 5 years) [110]. Among those with VTE, two-thirds were unprovoked. Further details regarding VEXAS syndrome are provided separately. (See "Autoinflammatory diseases mediated by NFkB and/or aberrant TNF activity", section on 'Vacuoles, E1 enzyme, X-linked, autoinflammatory, somatic (VEXAS) syndrome'.)
There is conflicting evidence concerning whether air pollution is [111-113] or is not [114,115] causally related to VTE development. (See "Overview of possible risk factors for cardiovascular disease", section on 'Air pollution'.)
Hospital admission rates for VTE are highest during the winter months and lowest during the summer months [116,117]. Possible explanations include vasoconstriction due to reduced activity or cold weather; superimposed infection; or seasonal variation in thrombogenic factors, including fibrinogen and factor VII activity [118], and active sun exposure [117].
The higher rate of VTE in Black Americans compared with White Americans is thought to be mostly explained by the higher prevalence of risk factors in Black Americans [119].
INHERITED THROMBOPHILIA —
A positive family history of venous thromboembolism (VTE) is a strong VTE risk factor (table 3) [120].
Common inherited hypercoagulable states — Among the inheritable deficiencies, the factor V Leiden and the prothrombin gene mutations together account for 50 to 60 percent of cases in White populations. Defects in protein S, protein C, and antithrombin (formerly known as antithrombin III) account for most of the remaining cases [121-124]. The relative risk for developing VTE is increased in people with the factor V Leiden (four- to fivefold) and prothrombin G20210A mutations (three- to fourfold) and those with deficiencies of antithrombin (16-fold), protein C (sevenfold), and protein S (fivefold) (table 3).
Each of these conditions is discussed separately:
●Factor V Leiden mutation (see "Factor V Leiden and activated protein C resistance")
●Prothrombin gene mutation (see "Prothrombin G20210A")
●Protein S deficiency (see "Protein S deficiency")
●Protein C deficiency (see "Protein C deficiency")
●Antithrombin deficiency (see "Antithrombin deficiency")
The evaluation of patients with established VTE for inherited thrombophilia is discussed separately. (See "Evaluating adult patients with established venous thromboembolism for acquired and inherited risk factors".)
Other genetic abnormalities of no or uncertain VTE risk — These disorders include the following:
●Heparin cofactor II deficiency – Heparin cofactor II is a thrombin inhibitor. Several families have been described with deficiency in this protein inherited as an autosomal dominant trait. Heterozygous individuals have plasma heparin cofactor II concentrations that are approximately 50 percent of normal values.
It is unclear if heparin cofactor II deficiency is a significant risk factor for thrombosis [125,126]. In one series of 305 patients with juvenile thromboembolic episodes, two patients had heparin cofactor II deficiency [126]. However, each patient had a second defect: the factor V Leiden mutation or protein C deficiency.
●Dysfibrinogenemia – Patients with dysfibrinogenemia have structural defects that cause alterations in converting fibrinogen to fibrin. Defects can be inherited or acquired. These disorders are discussed separately. (See "Disorders of fibrinogen".)
●Factor XII deficiency – Severe factor XII deficiency (factor XII activity <1 percent of normal) is inherited as an autosomal recessive trait. It prolongs the activated partial thromboplastin time, but is not associated with bleeding [127]. However, patients exhibit a thrombophilic tendency attributed to reduced plasma fibrinolytic activity [128]. Further information on factor XII deficiency is provided separately. (See "Rare inherited coagulation disorders".)
●Other genetic variants – Several genetic variants associated with an increased VTE risk have been found by candidate and genome-wide screens with odds ratios generally <1.5 [129-131]. These include variants in the genes for fibrinogen and factor XI. (See "Evaluating adult patients with established venous thromboembolism for acquired and inherited risk factors".)
Similarly, adults with supernumerary sex chromosome aneuploidies (ie, more than two sex chromosomes) are at increased risk of VTE compared with patients who have two sex chromosomes (1.3 versus 0.25 percent per person year; 10-year risk difference 8.8 percent) [132].
●Plasminogen and plasminogen activator inhibitor-1 (PAI-1) – Plasminogen deficiency has not been shown to be a risk factor for venous thrombosis. However, a 4G polymorphism in the PAI-1 promoter (designated 4G/5G) may be a weak risk factor when combined with other thrombophilic defects. (See "Plasminogen deficiency" and "Thrombotic and hemorrhagic disorders due to abnormal fibrinolysis".)
ANATOMIC RISK FACTORS FOR DEEP VEIN THROMBOSIS —
Several anatomic factors increase the risk of deep vein thrombosis (DVT) in the upper or lower extremities.
Varicose veins — Varicose veins are associated with an increased risk of DVT [133-135]. In one observational study, patients with varicose veins had an increased rate of DVT and pulmonary embolism (PE) compared with patients without varicose veins (6.6 versus 1.2 per 1000 person-years, hazard ratio [HR] 5.3 [DVT]; 0.48 versus 0.28 per 1000 person-years, HR 1.73 [PE]) [133]. Further studies are required to confirm this association and ensure that it is not due to confounding variables, such as smoking or obesity. (See "Approach to treating symptomatic superficial venous insufficiency".)
Paget-Schroetter syndrome — Paget-Schroetter syndrome, also called spontaneous upper extremity venous thrombosis, is usually due to an underlying compressive anomaly at the thoracic outlet. This subject is discussed separately. (See "Primary (spontaneous) upper extremity deep vein thrombosis" and "Brachial plexus syndromes", section on 'Thoracic outlet syndrome'.)
May-Thurner syndrome — May-Thurner syndrome (MTS; also known as iliac vein compression syndrome) is due to compression of the left common iliac vein between the overlying right common iliac artery and the underlying vertebral body. MTS has been associated with unprovoked left iliofemoral DVT or chronic venous insufficiency. MTS is discussed separately. (See "May-Thurner syndrome".)
Inferior vena cava abnormalities — Congenital venous malformations of the inferior vena cava (IVC), including agenesis, hypoplasia, or malformation, may lead to DVT [136-143]. In such cases, DVT primarily occurs in young patients and may be bilateral or recurrent or involve the iliac veins, a clinical picture similar to that of the inherited thrombophilias.
●In a series of 97 consecutive patients presenting with confirmed DVT of the lower extremities, 5 of the 31 with thrombotic occlusion of the iliac veins had an anomaly of the IVC. Thrombosis was bilateral in one and recurrent in two patients [140]. Patients with IVC abnormalities were younger at the time of presentation compared with those who did not have an IVC abnormality (25 versus 53 years).
●In one report of 10 cases of IVC agenesis-associated DVT (mean age 25 years), DVT followed intense and unusual physical activity in eight, was bilateral in six, and was localized to iliofemoral veins in nine [141].
ABNORMAL LEVELS OF CLOTTING FACTORS AND CHEMOKINES —
Elevated levels of select clotting factors and chemokines have been associated with an increased thrombotic risk (table 4). These measurements in patients with venous thromboembolism (VTE) have generally been made following a thrombotic event, so a post-thrombotic phenomenon cannot be entirely excluded. The basis for the elevated levels of these factors remains unclear and is rarely genetically based.
●Elevated factor VIII – Elevated plasma factor VIII coagulant activity (VIII:C) is an independent marker of increased thrombotic risk [144-148]. In one study, factor VIII:C levels >150 percent of normal had a fivefold increased risk of VTE compared with individuals with levels <100 percent [149].
Another study reported that the prevalence of elevated factor VIII:C levels in patients with unexplained thrombosis is approximately 25 percent [150].
An elevated factor VIII level may also be a strong thrombotic risk factor in Black patients. In a study of 100 Black patients with VTE, only 9 percent had an underlying genetic cause (eg, protein C or S deficiency, antithrombin deficiency) while 34 percent had VIII:C levels higher than the 90th percentile [151].
High factor VIII levels are not acute phase reactants and persist over time [152,153]. Elevated factor VIII levels appear to be constitutional with a heritable contribution [154-156], although the genetic determinant responsible for them has not been identified [157-159].
A rare partial duplication in the gene for factor VIII has been associated with markedly elevated factor VIII levels and venous thrombosis in two Italian families [160]. This duplication contains transcriptional activators that may upregulate messenger ribonucleic acid (mRNA) and protein expression.
●Other plasma components – A two- to threefold increased risk for VTE has been reported for altered levels of several plasma components, coagulant factors, anticoagulant factors, and inflammatory chemokines (table 4). Assays for some of these proteins are not widely available and the clinical utility of these abnormalities is uncertain. (See "Clinical use of coagulation tests", section on 'Shortened PT and/or aPTT'.)
•Elevated levels of the following have been described:
-Plasma factor IX antigen [161,162]
-Plasma factor XI antigen [163,164]
-Thrombin-activatable fibrinolysis inhibitor [165-167]
-Plasminogen activator inhibitor-1 [167]
-Interleukin 8 [168,169]
-Factor VII levels [156]
-Plasma fibronectin levels [170]
-Von Willebrand factor (VWF) [156,171,172]
-Fibrinogen [153,173,174] (see "Disorders of fibrinogen")
-Altered fibrin clot structure and function [175]
•Reduced levels of the following have been described:
-Tissue factor pathway inhibitor [176]
-Plasma fibrinolytic activity [167,177]
-Thrombomodulin [178]
●Single nucleotide polymorphisms (SNPs) – SNPs variations of the nucleotide sequence in the genome occurring in at least 1 percent of the population) and other genetic variations have been implicated as potential genetic contributors to the risk of VTE [178-186]. (See "Genetic testing".)
Several such SNPs were identified, including two within the factor XI gene locus, that may explain VTE associated with elevated factor XI levels [179,180,186].
●Non-O blood type – Patients with the non-O blood group (ie, groups A, B, and AB) have been shown to have a higher VTE risk than those with blood group O (odds ratios of 1.79 and 1.84) [187-189]. This may be related to associated differences in VWF and factor VIII levels between patients with O and non-O blood groups. (See "Pathophysiology of von Willebrand disease", section on 'Clearance and control of plasma VWF levels'.)
●Stabilin-2 (STAB2) variants – Genetic analysis has shown rare variants in the STAB2 gene that increase the risk for VTE [190]. STAB2 encodes Stabilin-2, an endothelial cell surface scavenger receptor that may lead to reduced clearance and higher levels of VWF in the blood.
●Factor IX Padua – A rare gain-of-function mutation in factor IX (R338L or factor IX Padua) was associated with an episode of deep vein thrombosis in a previously healthy 23-year-old male from Italy [161]. The plasma level of factor IX antigen in the proband was normal, but factor IX activity was approximately eight times the normal level.
UPPER EXTREMITY THROMBOSIS —
A major risk factor for developing deep vein thrombosis (DVT) of the upper extremity is the presence of indwelling venous catheters. A less common risk factor in patients with a spontaneous upper extremity DVT is anatomic abnormalities of the thoracic outlet causing axillosubclavian compression. These entities are discussed separately. (See "Catheter-related upper extremity venous thrombosis in adults" and "Primary (spontaneous) upper extremity deep vein thrombosis".)
INFORMATION FOR PATIENTS —
UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5th to 6th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10th to 12th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.
Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)
●Beyond the Basics topics (see "Patient education: Deep vein thrombosis (DVT) (Beyond the Basics)" and "Patient education: Pulmonary embolism (Beyond the Basics)" and "Patient education: Antiphospholipid syndrome (Beyond the Basics)")
SUMMARY
●Pathogenesis and risk factors – Virchow's triad is the underlying pathophysiology of thrombosis formation (stasis, endothelial injury, hypercoagulable state). Risk factors are identified in 80 percent of patients with venous thromboembolism (VTE), can be acquired or hereditary, and are often multiple in a given patient (table 1). Identifying risk factors raises the clinical suspicion for thrombosis and may influence treatment. (See 'Virchow's triad and risk factor prevalence' above.)
●Acquired – The major acquired risk factors for VTE include prior thromboembolism, active malignancy, (including myeloproliferative neoplasms), recent major surgery, trauma, immobilization, heart failure, older age (≥65 years), pregnancy, inflammatory bowel disease, exogenous estrogens, and antiphospholipid antibodies (table 1). (See 'Acquired risk factors' above.)
Less common etiologies include kidney diseases, hematologic diseases associated with hyperviscosity and leukostasis, and paroxysmal nocturnal hemoglobinuria.
Other miscellaneous causes include hyperhomocysteinemia, polycystic ovarian syndrome, ovarian hyperstimulation syndrome venous catheters, superficial thrombophlebitis, and several other conditions.
●Inherited thrombophilia – Factor V Leiden and prothrombin gene mutations are the most common inherited thrombophilias while defects in protein S, protein C, and antithrombin are less common (table 2 and table 3). (See 'Common inherited hypercoagulable states' above.)
Inherited thrombophilias are discussed in detail separately.
•(See "Factor V Leiden and activated protein C resistance".)
•(See "Prothrombin G20210A".)
•(See "Protein S deficiency".)
•(See "Protein C deficiency".)
•(See "Antithrombin deficiency".)
In other inheritable disorders, the risk is unclear. This includes heparin cofactor II deficiency, dysfibrinogenemia, and factor XII deficiency. (See 'Other genetic abnormalities of no or uncertain VTE risk' above.)
●Anatomic abnormalities – Several anatomic factors increase the risk of deep vein thrombosis in the upper or lower extremities including varicose veins; Paget-Schroetter syndrome (thoracic outlet compression); May-Thurner syndrome (iliac vein compression); or inferior vena cava agenesis, hypoplasia, or malformation. (See 'Anatomic risk factors for deep vein thrombosis' above and "May-Thurner syndrome" and "Primary (spontaneous) upper extremity deep vein thrombosis".)
●Abnormal levels of clotting factors and chemokines – Abnormal levels of some clotting factors and chemokines, including elevated levels of factors VIII, IX, and XI, thrombin-activatable fibrinolysis inhibitor, plasminogen activator inhibitor-1, and interleukin 8 have been associated with an increased thrombotic risk (table 4). (See 'Abnormal levels of clotting factors and chemokines' above.)