It is not surprising that risk of acute DVT increases with the number of risk factors that a person has. First of all, risk of DVT increases 1.9 times for each 10-year increase in age (Table 1). Other risk factors are surgery, trauma, malignancy, previous DVT, immobilization, primary (genetic)hypercoagulable states, oral contraceptives and hormone therapy, and other variable factors.

Table 1. Risk Factors for Acute Deep Venous Thrombosis

  Risk Factor Risk or Percent of Patients
  Age 1.9 risk increment for each 10-year increase from 20 to 80 years
 Surgery  
     Hip/knee 4861%
     Neurosurgery 24%
     General 19%
  Trauma 58%
     Femoral catheter placement 12%
  Malignancy
  (lung cancer, gastrointestinal tumors)
15%
  Previous thromboembolism 2-9%
  Primary (genetic) hypercoagulable states  
     Antithrombin, protein C/S deficiency 10xrisk
     Factor V Leiden 4x80 risk, depending on type
     Prothrombin 20210A 4x risk
     Increased factor VIII 6x risk
     Hyperhomocysteinemia
     (high blood levels of homocysteine)
2.5-4x risk
  Family history 2.9x risk
  Oral contraceptive use 2.9x risk
  Estrogen replacement 2-4x risk
  Immobilization  
     Bed rest of 3 days Start of increased incidence
     Confinement of 1, 2, and 4 weeks 15%, 77%, 94% increase in incidence
     Prolonged air or other confined travel Unclear
  Pregnancy and postpartum 0.075% of pregnancies; 2.3-6.1% per 1000 deliveries; 12% of trauma patients
  Antiphospholipid antibodies 2-6x risk
  Inflammatory bowel disease Occurs in 1.2-7.1% of patients
  Obesity, varicose veins, heart attack,
  congestive heart failure
All variable
   
Modified from Gloviczki P, Yao, JST, eds:  Handbook of Venous Disorders, 2nd ed. London: Arnold, 2001, p. 38.

 

Figure 1

Risk of recurrent thrombosis is greatest within the first 3 weeks after anticoagulant therapy, probably because of the difficulty in attaining constant levels of adequate anticoagulation (Figure 1).

 

Figure 1. Cumulative incidence of recurrent thrombotic events during the first 3 weeks of therapy. (Awaiting permission from Caps MT, Meissner MH, Tullis MJ, et al. Venous thrombus stability during acute phase of therapy. Vascular Medicine 1999;4:914.)