Risk Factors

For more information see the Scottish Intercollegiate Guidelines Network Guidelines on Prevention and Management of Venous Thromboembolism1  

People living with HIV
HIV infection1

Evidence suggests that patients with HIV have multiple risk factors and a 2- to 10-fold increased risk of venous thromboembolism (VTE) compared with the general population.2

Known risk factors include:

  • diagnosis of AIDS
  • low CD4+ cell count
  • protein S deficiency
  • protein C deficiency

Possible (unconfirmed) risk factors associated with HIV include:

  • protease inhibitor (PI) therapy
  • presence of active opportunistic infections
  • presence of antiphospholipid antibodies
General population
In the general population, the risk of thromboembolism rises exponentially with age, possibly as a result of increased immobility or coagulation.

  • <40 years – annual incidence of 1/10,000
  • 60-69 years – annual incidence of 1/1,000
  • >80 years – annual incidence of 1/100

The risk of thromboembolic disease is 2- to 3-fold higher among obese individuals (body mass index >30 kg/m2).

Varicose veins1

Patients with varicose veins have a 1.5- to 2.5-fold greater risk of developing thromboembolic disease after major general/orthopaedic surgery. The risk of developing thromboembolic disease after varicose vein surgery is not known.

Family History1

Regardless of their age, a patient’s risk of developing a thromboembolic disease is increased if they have at least one first-degree relative who developed the condition before the age of  50.


Abnormalities in the coagulation system can lead to a propensity to develop thromboembolic disease. These may include:

  • low levels of coagulation inhibitors (antithrombin, protein C or S)
  • activated protein C resistance (e.g. factor V Leiden)
  • high coagulation factors (I, II, including prothrombin G20210A, VIII, IX, XI)
  • antiphospholipid antibodies
  • high levels of homocysteine
  • elevated lipoprotein A (>300mg/L)

Other thrombotic states (non-HIV-infected population)1
  • Cancer

    • patients with cancer have a 5- to 7-fold higher risk of developing a first VTE and an increased risk of recurrent VTE. Risk varies according to the type of cancer. The risk of VTE may be increased further if the patient undergoes surgery or chemotherapy, or receives erythropoiesis-stimulating agents or a central venous catheter. 
  • Heart failure

    • patients with recent myocardial infarction or stroke are at increased risk of VTE.
  • Metabolic syndrome

    • patients with metabolic syndrome have a two-fold increased risk of VTE, compared with control subjects.
  • Severe acute infection  
  • Inflammatory bowel disease
  • Nephrotic syndrome
  • Myeloproliferative disease
  • Paraproteinemia
  • Behcet’s disease
  • Paroxysmal nocturnal hemoglobinuria
  • Sickle cell trait and sickle cell disease 

Combined oral contraceptives, hormone replacement therapy and antioestrogens1
  • Patients who take combined oral contraceptives have a 2- to 8-fold increased risk of VTE compared with non-users.
  • Oral estrogen hormone replacement therapy (HRT) users have a 2.5-fold increased VTE risk compared with non-users.
  • Raloxifene and tamoxifen are associated with a 2- to 3-fold increased VTE risk.

There is currently no evidence to suggest that progesterone-only oral contraceptives are associated with an increased risk of VTE; however, the use of high-dose progestogens to treat gynecological problems has been associated with a six-fold increased VTE risk.


Pregnant women have approximately 10-fold increased risk of thromboembolism during pregnancy and a 25-fold increased risk during the puerperium, compared with non-pregnant/non-puerperal women.

Immobility due to travel1

Patients remaining immobile for long periods (e.g. during air-travel) have a 2- to 3-fold increased risk of VTE.


Acute trauma, acute illness and surgery are associated with a 10-fold increased VTE risk.


A 2- to 3-fold increased risk of postoperative VTE has been reported with the use of general anaesthesia, compared with spinal/epidural anesthesia.


  1. Scottish Intercollegiate Guidelines Network Guidelines on Prevention and Management of Venous Thromboembolism. 2010. Accessed 27 April 2011.
  2. Kiser KL, Badowski ME. Risk factors for venous thromboembolism in patients with human immunodeficiency virus infection. Pharmacotherapy. 2010;30(12):1292-1302.


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