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Individuals who may benefit from genetic testing for hereditary thrombophilia include:
- individuals with venous thromboembolism (VTE) <50 years of age without the following
- major transient risk factor (eg surgery, immobility, trauma)
- oestrogen provocation (eg pregnancy, prescribed oestrogens)
- individuals with VTE <50 years of age in an unusual site (eg central nervous system, abdominal veins, upper limb)1–3
- pregnant women who have had a previous episode of VTE or who have a strong family history of VTE (≥2 family members).1,4
Routine genetic testing for hereditary thrombophilia in individuals without any of the above features is not recommended in general practice.1
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.
What do I need to know?
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
Testing practices for hereditary thrombophilia are variable across Australia, in part due a to lack of local evidence-based guidelines.2
Factor V Leiden and prothrombin variant genetic testing is only available on the Medicare Benefits Schedule (MBS) if the patient has a:9
- personal history of VTE
- family histroy of a diagnosed inherited thrombophilic condition.
When should I refer?
Refer women with hereditary thrombophilia who are pregnant or thinking about pregnancy. Management of hereditary thrombophilia in pregnancy requires specialised risk assessment, and patients should be under the direction of a specialist haematologist, obstetric physician or obstetrician.4,5
Patients diagnosed with hereditary thrombophilia should be encouraged to inform all first-degree relatives of increased risk; however, the benefit of cascade screening of relatives is uncertain.2,5,8,10
Resources for patients
Centre for Genetics Education, Fact sheet 49: Blood clotting conditions (hereditary thrombophilias)
NHS Choices (UK), Thrombophilia
Varga E, The genetics of thrombophilia