The incidence of venous thromboembolism among Factor V Leiden carriers: a community-based cohort study

While Factor V (FV) Leiden is a risk factor for venous thromboembolisin (VTE), the incidence of VTE among FV Leiden carriers is uncertain. The objective of the study was to estimate the overall age-specific and pregnancy-related VTE incidence and the relative risk among FV Leiden carriers. In a community-based sample of 3424 south-eastern Minnesota residents, 230 (6.7%) were genotyped as FV Leiden carriers; 220 carriers (mean age = 68 years) could be matched to a noncarrier on age, gender, ethnicity and length of medical history. We performed a retrospective cohort study of carriers and noncarriers by reviewing the complete medical records in the community for demographic and baseline characteristics, pregnancies and live births, and first lifetime VTE. Over 14 722 person-years, 24 (10.9%) carriers developed VTE [overall incidence = 163 (95% CI 104, 242) per 100 000 person-years]. VTE incidence rates for ages 15-29, 30-44, 45-59 and greater than or equal to60 years were 0, 61, 244 and 764 per 100 000 person-years, respectively (cumulative VTE incidence at age 65 years = 6.3%). VTE incidence for carriers did not differ significantly from that for non-carriers except for those greater than or equal to60 years old (relative risk = 3.6; 95% Cl 2.0, 6.0). There were 311 live births among 130 women carriers; no VTE events occurred during pregnancy or postpartum [incidence = 0 (95% CI 0, 1186) per 100 000 women-years). Most FV Leiden carriers do not develop VTE. Among all carriers, those ! 60 years old are at the highest risk for VTE. The incidence of VTE among asymptornatic women carriers during pregnancy is low and insufficient to warrant prophylaxis.