A lower risk of recurrent venous thrombosis in women compared with men is explained by sex-specific risk factors at time of first venous thrombosis in thrombophilic families

Abstract

Why men appear to have an increased risk of recurrent venous thrombosis compared with women is unknown. In a cohort study of families with thrombophilia, lifetime risk of recurrent venous thrombosis was assessed in men and women (n = 816). Adjusted relative risk of recurrence was 1.6 (95% CI, 1.3-2.0) in men compared with women. Women were younger at time of their first event (mean, 34 years vs 44 years; P < .001) and at time of recurrence (40 years vs 48 years, P < .001). After excluding provoked first and recurrent venous thrombosis, adjusted relative risk was 1.2 (95% CI, 0.8-1.7), although mean age at recurrence was comparable in men and women (50 years vs 49 years, P = .595). In women with a hormonal first event, median interval between first event and recurrence was 10.4 years versus 2.7 years in men (P < .001). This difference was not observed when only unprovoked events were considered (P = .938). The difference in lifetime risk of recurrent venous thrombosis between men and women in thrombophilic families can be explained by a younger age of women at time of first venous thrombosis due to hormonal risk factors, and a longer interval between a provoked first episode of venous thrombosis and recurrence in women.