Selective Use of D-Dimer Test for Deep Vein Thrombosis

D-dimer testing is sensitive but not specific for DVT and changing the threshold level for a positive test result based on risk for DVT might improve the tradeoff between sensitivity and specificity and reduce the need for testing.

Scientists from McMaster University, (Hamilton, ON, Canada) randomly assigned 1,723 outpatients presenting for the first time with symptoms of DVT to selective testing for D-dimer for patients with low or moderate clinical pretest probability of DVT. Some patients with high clinical pretest probability had venous ultrasonograpy without D-dimer testing and some patients presenting with symptoms had uniform testing. The study groups were all consecutive symptomatic patients with a first episode of suspected DVT from five different hospitals.

Selective testing of 860 patients, defined as d-dimer testing for outpatients with low or moderate clinical pretest probability (C-PTP), where DVT excluded at d-dimer levels of equal to or less than 1.0 µg/mL, a low C-PTP or equal to or less than 0.5 µg/mL, moderate C-PTP. The groups who had venous ultrasonography without d-dimer testing for outpatients with high C-PTP and inpatients, or the 863 uniform testing defined as d-dimer testing for all participants where DVT was excluded at d-dimer levels of less than 0.51 µg/mL.

The incidence of symptomatic venous thromboembolism at three months was 0.5% in both study groups. Selective testing reduced the proportion of patients who required d-dimer testing by 21.8% and reduced the proportion that required ultrasonography by 7.6 % overall and by 21.0% in outpatients with low C-PTP. The authors concluded that a selective d-dimer testing strategy seems as safe as and more efficient than having everyone undergo d-dimer testing when diagnosing a first episode of suspected DVT. The study was published on January 15, 2013, in the journal Annals of Internal Medicine.

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