Factor XI deficiency is associated with lower risk for cardiovascular and venous thromboembolism events.

Factor XI deficiency is one of the rare inherited coagulation factor deficiencies. However, its incidence is high within the Ashkenazi Jewish community. Because factor XI displays both procoagulant and antifibrinolytic activities, it has been postulated that an underlying cardiovascular benefit may exist with factor XI deficiency. This historical cohort study was performed using the electronic database of Clalit Health Services, the largest health care provider in Israel. All adults tested for factor XI activity between 2002 and 2014 were included in the study. Factor XI activity was classified into 3 categories: normal (activity >50%), mild deficiency (activity = 30%-50%), and moderate-severe deficiency (activity ≤30%). The cohort was followed until 31 December 2015 for incidence of cardiovascular events (composite of myocardial infarction, stroke, and transient ischemic attack) and venous thromboembolism (VTE). Of the 10 193 included patients, 8958 (88.9%) had normal factor XI activity, 690 (6.8%) had mild deficiency, and 542 (5.3%) had moderate-severe deficiency. Compared with individuals with normal activity, the adjusted hazard ratio (HR) for cardiovascular events was 0.52 (95% confidence interval [CI], 0.31-0.87) in those with mild deficiency, and 0.57 (95% CI, 0.35-0.93) in those with moderate-severe factor XI deficiency. The incidence of VTE was lower in those with factor XI deficiency (activity <50%) compared with those with normal activity; adjusted HR = 0.26 (95% CI, 0.08-0.84). In summary, factor XI deficiency is associated with decreased incidence of cardiovascular events and VTE.