Summary

The risk of spontaneous or risk-period related venous thromboembolismin family members of symptomatic carriers of antithrombin(AT), protein C (PC) or protein S (PS) defects, as well as of the FactorV Leiden mutation is still undefined. We performed a retrospectivecohort study in family members (n = 793) of unselected patients with adocumented venous thromboembolism and one of these deficiencies tomake an estimate of this risk. The annual incidences of total andspontaneous venous thromboembolic events in carriers of AT, PC or PSdefects (n = 181) were 1.01% and 0.40%, respectively, as compared to0.10% and 0.04% in non-carriers, respectively (relative risks both10.6). In carriers of Factor V Leiden (n = 224), the annual incidences oftotal and spontaneous venous thromboembolism were 0.28% and0.11%, respectively, as compared to 0.09% and 0.04% in non-carriers,respectively (relative risks 2.8 and 2.5). Additional risk factors (immobilisation,surgery and trauma; oral contraceptive use; and pregnancy/post-partum) increased the risk of thrombosis in carriers of AT, PC andPS defects as compared to non-carriers (relative risks 8.3, 6.4 and8.2, respectively). Oral contraceptive use and pregnancy/ post-partumperiod increased the risk of thrombosis in carriers of Factor V Leidento 3.3-fold and 4.2-fold, respectively, whereas other risk factors hadonly a minor effect.These data lend some support to the practice of screening familymembers of symptomatic carriers of a AT, PC and PS deficiency. Forfamily members of symptomatic carriers of Factor V Leiden, screeningdoes not seem to be justified except for women in fertile age.