Total tissue factor pathway inhibitor and venous thrombosis: The longitudinal investigation of thromboembolism etiology

Tissue factor pathway inhibitor (TFPI) inhibits tissue factor, a potent coagulation initiator. Limited evidence suggests that low TFPI levels are associated with increased risk of venous thromboembolism (VTE). We measured total TFPI in a nested case-control study in the Longitudinal Investigation of Thromboembolism Etiology. Control subjects were frequency matched 2:1 to cases on age, sex, race, and cohort. Odds ratios (ORs) for VTE by TFPI levels were computed using logistic regression models adjusting for age, race, sex, coagulation factors (factors VII, VIII, IX, XI, D-dimer), and body mass index (BMI). To evaluate for greater than additive interactions, we calculated the percent relative excess risk due to interaction between TFPI and other VTE risk factors. A total of 534 cases of VTE occurred and matched to 1,091 controls. Mean baseline TFPI in ng/ml (standard deviation) in those who developed VTE and controls was 36.4 (12.8) and 35.0 (11.1), respectively. Higher TFPI was associated with male sex, age, BMI, factors VII, VIII, IX, XI, and D-dimer. TFPI level did not differ by ethnicity, factor V Leiden, or prothrombin G20210A. Compared with those in the upper 95%, the bottom 5% of TFPI had an age-, sex-, race-, and study-adjusted OR (95% CI) of 1.35 (0.86, 2.12) for VTE. Adjusting for factors VII, VIII, IX, and XI the OR was 1.93 (1.05, 3.53). Further addition of D-dimer and BMI to this model decreased the OR to 1.70 (0.98, 2.93). Low TFPI did not demonstrate greater than additive interaction with other VTE risk factors.