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Question 37#

A 60-year-old woman develops deep venous thrombosis after a 14-hour plane flight from New Zealand. The diagnosis is confirmed by a venous Doppler. There is no evidence of pulmonary embolism, and she is started on subcutaneous low-molecular-weight heparin. She has no family history of venous thrombosis, and she is on no medications that would increase her risk of clotting. In addition to routine monitoring of coagulation parameters and a CBC,

what diagnostic tests should be ordered next? 

A. Functional test for factor V Leiden (activated protein C resistance)
B. Protein C, protein S, and antithrombin III levels
C. Antiphospholipid antibody test
D. Genetic testing for prothrombin G20210A gene mutation
E. No further testing

Correct Answer is E

Comment:

Testing for thrombophilia is generally reserved for patients who develop unprovoked venous thromboses, especially when those events occur before age 50 in a patient with a positive family history of abnormal clotting. This patient should simply be treated with low-molecular-weight heparin followed by 3 to 6 months of warfarin in the standard fashion. If she develops recurrent DVT, thrombophilia testing would be considered. The prothrombin gene mutation (G20210A) and factor V Leiden are the commonest genetic factors associated with DVT, but they cause only a modestly increased risk of DVT and their presence may not change the management of the patient. Patients with factor V Leiden who are taking oral contraceptives have a 35-fold increased risk of DVT, but OCPs should be avoided if possible in women with any prior history of DVT. Protein C, S, and AT III deficiencies confer a much greater risk, but are significantly less common. Their presence will usually be identified by the history including family history. Remember that these genetic conditions have been associated with an increased risk of venous, not arterial, thrombosis. Only the antiphospholipid antibody syndrome and elevated homocysteine levels have been associated with arterial thromboses.