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Letter to the Editor: D-Dimer Adds Nothing to Evaluation

doi: 10.1097/01.EEM.0000515704.82203.a0
Letter to the Editor

Editor:

I have issues with the article, “Think Twice about DVT and a Negative US,” by Christine Butts, MD. (EMN 2017;39[2]:1; http://bit.ly/2kZRpMt.)

Granted, the initial evaluation of this patient was reasonable — getting a sonogram on a patient with a unilateral swollen leg and no anticoagulation because it was negative. But the usual algorithm for this condition on the repeat visit is to do a sonogram and then a venogram if there is a high level of suspicion of DVT. I have never seen this done, but that's how it was taught in residency 20 years ago. This case mentions that a CT with IV contrast was done to check for a deep infection. There still isn't any mention of the possibility of a DVT being present. Does a CT angiogram of the leg differ in the potential etiologies versus a CT with IV contrast? I think it does.

Even if this test weren't ordered on this patient, where does adding a D-dimer come into play? This is a blood test that would be done in a low-risk patient to help decide whether to proceed on the DVT workup. An elevated D-dimer in this case adds absolutely nothing to this evaluation. In fact, the elevated D-dimer should have pushed the evaluator even more toward a venogram or CT angiogram. Neither was done here. It was actually just dumb luck, which we emergency physicians rely on quite often, that a DVT on the CT with IV contrast was found.

Any thoughts, or am I barking up the wrong tree here?

Jeff Schaffer, MD

Plano, TX

Dr. Butts responds: Dr. Schaffer raises some excellent points, including that he was taught the algorithm but had never seen it, and that was my goal in writing about this. Many of us aren't familiar with the validated DVT algorithm, the sensitivity of ultrasound for this condition, or even what type of ultrasound is performed at our hospitals. A lot of us have been performing half an evaluation of patients based on bits and pieces of the algorithm and getting lucky that we haven't missed one. A rule-out test is only as good as its sensitivity, and I'd argue limited compression ultrasound in these high-probability patients doesn't pass muster.

I do think D-dimer has a role, certainly when it's negative but also as an additional marker of clinical suspicion. As Dr. Schaffer so astutely points out, a patient with a markedly elevated D-dimer with high clinical suspicion should prompt the clinician to keep searching when the ultrasound is negative because something is obviously being missed. In the case I referenced, the clinician searched further by ordering a CT with contrast and, I would agree, got lucky. But I think that many others would have gone looking for another diagnosis as well because of the faith placed in the negative ultrasound. A case I wrote about last year was also based on over-reliance on ultrasound to rule out DVT and resulted in the death of a young woman. (EMN 2016;38[1]:1; http://bit.ly/2hm0MrH.) Thank you for raising some great points and continuing the discussion.

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