Testing for rare causes of thrombophilia

Mark Crowther, MD, MSc, is a professor of medicine, chair of the Department of Medicine, and Leo Pharma Chair in Thromboembolism Research at McMaster University.

In what situations should we perform additional testing for thrombophilia in patients without antiphospholipid syndrome and without any of the 5 basic congenital thrombophilias? What tests to order? Should they include the activity of coagulation factors VIII, IX, and X, and evaluation of the fibrinolytic system (TAFI, plasminogen, PAI-1 activity)?

Thrombophilia testing is a real problem because the most common 5 abnormalities, that is, factor V Leiden; the prothrombin gene mutation; and deficiencies in protein C, protein S, and antithrombin probably constitute the large majority of caused episodes of venous thromboembolism.

However, we very rarely test for these, and if we very rarely test for the common ones, it’s extraordinarily unusual for us to test for the very rare thrombophilias. So in fact, I would say that almost never should we even be considering testing for these rare things. We never test for coagulation factor VIII and IX levels—we simply don’t do it—and we would only test for things like homocysteine or other rare causes in very appropriate settings. For example, in the setting of consanguinity, we might think about hyperhomocysteinemia, which might be a cause of venous or arterial thrombosis. In fact, in the talk that I am going to be doing at this conference [McMaster International Review Course in Internal Medicine] on thrombophilia, I’m going to focus on some of these very rare causes of thrombophilia, which I would only consider in extraordinarily unusual but very specific clinical circumstances.

So the message is, in general, thrombophilia testing is vastly overused, and if the thrombophilia testing is not going to affect our decisions with respect to management, we would recommend against its use.