1. SECTIONS:
2. preface & acknowledgements
3. genetics at a glance
4. contacts, support & testing
5. testing & pregnancy
6. newborn screening
7. cancer in the family
8. cardiovascular conditions
9. chromosomal conditions
10. clotting & bleeding conditions
11. cystic fibrosis
12. diabetes
13. fragile X syndrome and other causes of developmental delay
14. haemoglobinopathies
15. hereditary haemochromatosis
16. neurofibromatosis
17. neurological conditions
18. psychiatric conditions
19. genetics in practice
20. emerging genetic technologies
21. glossary

Identifying individuals at risk of thrombophilia

 

1. Screening for thrombophilia should be considered in individuals with these characteristics:
2. DVT at <50 years
3. Spontaneous thrombosis in absence of recognised risk factors
4. Recurrent thrombosis
5. Family history of thrombosis
6. Thrombosis in unusual sites, eg CNS, abdominal veins, upper limb
7. Stillbirth or fetal death in utero
8. Factor V Leiden and prothrombin variant genetic testing is available on the MBS only if the patient has:
9. A personal history of DVT, or
10. A family history of a diagnosed inherited thrombophilic condition

 

Table 2

Prevalence of hereditary thrombophilias in the general population and approximate prevalence in individuals with venous thromboembolism

 

Table 3

Tests available for hereditary thrombophilias

 

Contraception and thrombophilia

1. Oestrogen-containing oral contraceptives or hormone replacement therapy increase the risk of VTE by
   2 to 4-fold and are relatively contra-indicated in women with hereditary thrombophilia.
2. Third generation combined pills are more thrombogenic than second generation preparations.
3. Decisions regarding oestrogen use should be made on an individual basis, after a risk-benefit analysis
   has been performed.
4. Factors that should be considered when prescribing the combined oral contraceptive pill include:
5. Past or family history of VTE
6. Other risk factors for VTE
7. Suitability of alternative means of contraception
8. Patient preference
9. Patient compliance
10. Advice should be sought from a specialist haematologist and/or family planning expert if required.

 

Note: Screening all women for hereditary thrombophilias before commencing oestrogen has not been shown to be cost effective. With regard to factor V Leiden, 20,000 women would need to be screened in order to prevent one DVT, while 2 million women require screening to prevent one death from pulmonary embolism. Rather, prior to prescribing oestrogens, practitioners should take a careful history with respect to past medical and family history and additional risk factors for thrombosis. Screening can then be targeted to those women who appear to be most at risk of thrombophilia.

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