Ask Dr. Stephan Moll

These questions have been submitted by folks on the mailing list and answered by Dr. Moll, Director of the Thrombophilia Program at the Carolina Cardiovascular Biology Center, Department of Medicine, Division of Hematology-Oncology, UNC Chapel Hill (North Carolina, USA). Why am I doing this?

19. D-dimer

Q: "What is a D-dimer test? How would it be used in conjunction with someone having factor V Leiden? How long does it take to return to normal?"

A: The D-dimer test is a blood test that examines, whether a certain breakdown product of blood clots, the so-called D-dimer, is present in the bloodstream. Whenever we clot, our body immediately starts to break down part of the clot and D-dimers start to appear in the blood. A negative test excludes the presence of a major blood clot in many patients and may make a Doppler ultrasound, venogram, or lung scan examination unnecessary.

A negative D-dimer test result may be helpful in excluding the presence of a blood clot. A positive test, on the other hand, is not, since it can be due to many things other than thrombosis (for example liver disease, trauma, surgery, pregnancy, infection); it, therefore, does not confirm the presence of a clot. In patients who have had a clot in the past, who are known to have a clotting disorder, or in whom the physician has a high suspicion for a thrombosis, the D-dimer test is not reliable and should not be used; in these patients one should go straight to obtaining an imaging study (Doppler ultrasound, venogram, or lung scan). The D-dimer test can return to normal within a few days to a week, but that depends on how elevated the test-level was to begin with and whether there are other reasons for the level to be elevated.

Recent data indicate that in the patient who has had a deep vein thrombosis (DVT) and has been treated with warfarin (=coumadin®) for a few months, a positive D-dimer indicates a higher risk for recurrent DVT if warfarin (=coumadin) is stopped (ref. 3,4). In these patients one may, therefore, consider more aggressive treatment with blood thinners, i.e. long-term full-dose warfarin (target INR 2.0-3.0) rather than low-dose warfarin or discontinuation of warfarin.

Personal comment: In patients with a history of one spontaneous deep vein thrombosis I often recommend 6 months of full dose warfarin (target INR 2.0-3.0). At the end of the 6 months I obtain a D-dimer test. If it is negative I discuss low-dose warfarin (target INR 1.5-2.0) with the patient, based on the PREVENT trial results (ref. 1). If the D-dimer is positive, I discuss full-dose warfarin (target INR 2.0-3.0), based on the ELATE trial results (ref. 2).

References:

1. PREVENT trial: Ridker PM et al.: "Long-term, low intensity warfarin therapy for the prevention of recurrent venous thromboembolism". New England Journal of Medicine 2003;348:1425-34.
2. ELATE trial: Kearon C et al.: "Comparison of low-intensity warfarin therapy with conventional-intensity warfarin therapy for long-term prevention of recurrent venous thromboembolism". New England Journal; of Medicine 2003;349:631-9.
3. Fattorini A et al.: "Risk of DVT recurrence: high negative predictive value of D-dimer performed during oral anticoagulation". Thrombosis and Haemostasis 2002;88:162-3.
4. Palareti G et al.: "Predictive value of d-dimer test for recurrent venous thromboembolism after anticoagulation withdrawal in subjects with a previous idiopathic event and in carriers of congenital thrombophilia". Circulation 2003;108:313-318.

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