A study from France suggests that women using hormone therapy have an increased production of thrombin and are therefore at higher risk for venous thromboembolism (VTE). According to the July issue of Menopause, Dr. Pierre-Yves Scarabin and his research team at the University of Paris XI in France measured prothrombin production, coagulation factors and inhibitors in 115 healthy postmenopausal women. Based on their use of hormone therapy, these women were divided into three groups: a non-use group (n=38), an oral estrogen and progestin use group (n=38), and a transdermal estrogen and progestin group use group (n=39). Calibration of the automated thrombogram showed a significant increase in mean peak and a much shorter lag time in the oral estrogen group compared to the non-use and transdermal estrogen groups (2.9 min vs. 3.4, 3.4 min). In addition, women using oral estrogen had significantly higher endogenous prothrombin potential (ETP) than women who had never used hormone therapy. The group also found that women who combined transdermal estrogen with progestin had significantly higher prothrombin production (ETP and peak height) compared to non-users and women who combined transdermal estrogen with progesterone. Notably, levels of factor II (prothrombin) were also significantly higher in the former. Since prothrombin is a determinant of thrombin production, the difference in prothrombin levels between women using transdermal estrogen combined with progestin and those using progesterone in combination resulted in differences in thrombin production between the two groups. The group did not observe a significant increase in any other procoagulant factors or a significant decrease in coagulation inhibitors. Both these findings and the epidemiological evidence suggest that women using oral estrogens have a higher risk of VTE than women using transdermally absorbed estrogens. Dr. Scarabin also noted that further studies are needed to determine the effect of progestins on surrogate indicators of VTE and to examine how and to what extent thrombin generation increases the risk of venous thromboembolism in users of hormone therapy.