RESUMO
The cumulative thrombotic risk of Factor V (FV) Leiden and oral contraceptives (OC) recommends screening for the mutation. Assuming that a family history of thrombosis increases the patient's likelihood of bearing FV Leiden, a selective rather than universal screening would be performed. We studied the utility of a family history of thrombosis for screening of FV Leiden before prescription of OC and, furthermore, the utility of screening even if oral contraception is favoured. 101 patients who had their first and single thromboembolic event while using OC were interviewed. 609 women without any history of thromboembolism recruited by gynecologists completed a standard questionnaire. 101 of these women, age-matched and currently using OC, were selected for a case-control study. Regarding patients with previous thromboembolism, a family history in a first-degree relative had a positive predictive value (PPV) of only 14% for FV Leiden. A PPV of 12% was calculated by investigating the 609 thrombosis-free women. Inherited FV Leiden (odds ratio = 4.9) and acquired risk factors (odds ratio = 10.1) were both found to be the most prominent, but independent additional risks. Nevertheless, FV Leiden carriers, both heterozygotes and homozygotes, did not suffer earlier from thromboembolism than patients without the mutation. In conclusion, family history is an unreliable criterion to detect FV Leiden carriers. Screening for factor V Leiden can be worthwhile even if the advantages of oral contraception are higher assessed than the thrombotic risk. Affected women knowing about their additional risk could contribute to the prevention of thrombosis in risk situations.
PIP: The cumulative thrombotic risk of Factor V Leiden (FVL) and oral contraceptive (OC) use raises the possibility of either selective or universal screening for this mutation before OCs are prescribed. Family history of venous thromboembolism as a criterion to detect FVL carriers was evaluated in a case-control study of 101 women from Bavaria, Germany, who had their first and single thromboembolic event while using OCs and 101 healthy age-matched OC users. A questionnaire was administered to a broader group of 609 OC users without a history of thromboembolism. Analysis of the 609 women revealed a 7.4% prevalence of FVL, but no association between this mutation and a family history of thromboembolism. Among women with a previous thromboembolism, a family history in a first-degree relative had a positive predictive value of only 14% for FVL. The sensitivity of family history was under 50%. 35% of cases compared with 8% of controls carried the FVL mutation. The most significant independent risk factors of thromboembolism were inherited FVL (odds ratio, 4.9) and acquired risk factors--i.e., surgery, leg fractures, distortions, confinement to bed for more than 1 week, or a restricted sitting position more than 6 hours in the 4 weeks before the index date (odds ratio, 10.1). Both heterozygote and homozygote FVL carriers did not suffer earlier from thromboembolism than patients without the mutation. These findings indicate that family history is not an effective predictor of FVL. However, even if the advantages of OC use are greater than the thrombotic risk, screening for FVL may be indicated to permit high-risk women to take preventive action.