Venous Blood Clots: Sex Difference in Risk Explained Interview with:
Dr. W.M. Lijfering, MD, PhD Department of Clinical Epidemiology, C7-P-89 Leiden University Medical Center PO Box 9600 2300 RC LeidenDr. W.M. Lijfering, MD, PhD
Department of Clinical Epidemiology, C7-P-89
Leiden University Medical Center
PO Box 9600
2300 RC Leiden What are the main findings of the study?

Dr. Lijfering: In this study we found that the risk of a first venous thrombosis* is two-fold higher in men than in women once female reproductive risk factors for venous thrombosis are taken into account (odds ratio 1.9, 95% CI 1.7-2.2). These results were found in all age categories (18-70 years) and were not affected by adjustment for body mass index and smoking, or by excluding participants with malignancy. Were any of the findings unexpected?

Dr. Lijfering: This is the first study that explains why the crude annual risk of first venous thrombosis is equal in men and women, yet the crude annual risk for a recurrent event is twice as high in men as compared with women. Women often stop taking oral contraceptives after a first venous thrombotic event or receive thromboprophylaxis when being pregnant. Hence, they are no longer prone to recurrent thrombotic events that are due to these reproductive factors. For a first event this is very different. Approximately 50% of women of reproductive ages experience a first venous thrombosis while being exposed to reproductive risk factors. Therefore our hypothesis was that a risk difference between the sexes is masked by female exposure to reproductive factors, which we confirmed in our study. What should clinicians and patients take away from your report?

Dr. Lijfering: This finding, which is in line with the findings of previous studies that showed that venous thrombosis recurs twice as often in men as in women, suggests that the intrinsic risk of venous thrombosis is higher in men than in women. Prediction models for recurrent venous thrombosis already advocate differential treatment strategies for men and women after a first venous thrombosis. From our results it seems that a differential approach to the prevention of first venous thrombosis in men and in women without reproductive risk factors may also be indicated. For instance, men may benefit from a lower threshold for prophylactic treatment than women without reproductive risk factors when encountering high risk situations for venous thrombosis. Male sex could be included in a prediction model in the same way as, for example, oral contraceptive use in women is sometimes included now. Alternatively, men may require a higher dose of prophylactic anticoagulation therapy than women without reproductive risk factors in order to reduce their venous thrombosis risk to the same extent. What recommendations do you have for future research as a result of this study?

Dr. Lijfering: It is important that future studies focus on the sex-specific risk and prevention of first venous thrombosis in order to identify which factors can be targeted to reduce the higher risk of venous thrombosis in men.


Sex Difference in Risk of Second but not of First Venous Thrombosis: Paradox Explained
Rachel E. J. Roach, Willem M. Lijfering, Frits R. Rosendaal, Suzanne C. Cannegieter, and Saskia le Cessie
Circulation. 2013;CIRCULATIONAHA.113.004768published online before print October 21 2013, doi:10.1161/CIRCULATIONAHA.113.004768


* Editor’s note: ‘venous thrombosis’ is a term for blood clot in the veins


Last Updated on November 1, 2013 by Marie Benz MD FAAD