Tuesday, September 10, 2013

Ruling out DVT: doppler or D-dimer?

- Jennifer Middleton, MD, MPH

Yesterday I saw an older patient with a swollen leg. Although I was reasonably confident that the swelling and pain was due to an early cellulitis, I still felt compelled to rule out a deep venous thrombosis (DVT). I ordered a stat ultrasound doppler of the leg, which was negative for DVT. I was left wondering if I shouldn't have wasted the patient's time and his insurance dollars on this test; I wasn't terribly worried about a DVT, but I also knew that I couldn't afford to miss one.

One of the POEMs in AFP last week reviewed a recent article from the Annals of Internal Medicine regarding testing for DVT.  The researchers evaluated the use of Wells' criteria to determine whether ultrasound (doppler) or a D-dimer was used first to evaluate for possible DVT.  The researchers divided the patients into two groups; one group consisted of outpatients with a low or moderate pre-test probability according to their Wells' score, and one group consisted of outpatients with a high pre-test score along with inpatients.  The patients in the first group with a positive D-dimer went on to ultrasound.  They found that stratifying patients by pre-test probability decreased the use of both D-dimer and ultrasound but did not negatively affect patient outcomes.

I know I should use clinical decision rules like the Wells criteria more often to help me eliminate unnecessary testing; there are a few rules that I do use regularly, but for less frequent diagnoses like this one, I often forget to look for an applicable rule.  There are many inexpensive smartphone apps that can make this process easier for clinicians, too.  I suspect that my patient yesterday would have preferred a quick blood test in the office instead of having to trek over to the hospital's vascular lab.  It seems, though, when I'm in the middle of a busy office session, that I often only think about using these tools after the day is done.  This POEM was an excellent reminder to me to think about incorporating these tools more into my everyday decision-making process.

There is a useful AFP by Topic about DVT and Pulmonary Embolism if you'd like more information about this topic.  And, here's the original study that validated Wells' criteria for DVT.

How are you currently working up possible DVTs?  Is it realistic to integrate the use of clinical calculators into your day-to-day practice?

2 comments:

  1. To play "Devil's Advocate" - just to be aware that as we cast a bigger and bigger "net" trying to catch any and everything that might have the slightest chance of being a DVT - the prevalence of disease in the population we are testing continues to decrease. As we arrive in an extremely low prevalence of DVT population - positive D-Dimers become more and more likely to be false positives. This is not benign - as it leads to more and more additional tests that may not be necessary (not to mention expense). There is radiation with Chest CT scans ...

    Bottom Line: There is no perfect test. There is no perfection. If you really think the patient has cellulitis - they probably do. As long as you maintain healthy respect for the clinical reality that sometimes you won't feel comfortable on clinical grounds what the diagnosis is - and do testing in those patients - you'll probably be on the mark at much less expense and with fewer unneeded tests.

    ReplyDelete
  2. Thanks very much for sharing your thoughts! Despite the growing number of clinical decision rules & tools available, I agree with you that our clinical judgment still is often our only source to determine pre-test probability.

    ReplyDelete