Individuals with hereditary thrombophilia have an increased tendency to develop blood clots.
There are a number of different types of hereditary thrombophilia conditions (Box 1). At least half of thrombotic episodes in individuals with hereditary thrombophilia occur during periods of increased risk, such as during pregnancy, immobilisation or surgery.5
The risk of VTE in women taking a low-dose combined oral contraceptive (COC; <35 ug ethinyl oestradiol) is increased two to three times, compared with non-users. Despite this increase in risk, there is no indication for routine screening of women prior to prescribing a COC.5,7,8
Box 1. Major hereditary thrombophilia conditions6
Group 1 conditions – Due to a defect or deficiency of an anticoagulant protein:
- Antithrombin deficiency
- Protein C deficiency
- Protein S deficiency
Group 2 conditions – Due to genetic mutations that result in an increased tendency towards thrombosis:
- Activated protein C resistance
- Factor V Leiden
- Prothrombin gene variant
- Elevated levels of factors VIII, IX and XI
The risk of thrombosis is higher for patients with Group 1 conditions than Group 2 conditions. Group 2 conditions occur approximately five times more frequently than Group 1 conditions.