Selective D-dimer testing best for DVT diagnosis

Troy Brown

January 15, 2013

Hamilton, ON - It is best to base D-dimer testing on a patient's clinical pretest probability (C-PTP) for deep vein thrombosis (DVT), rather than testing all patients who present with symptoms of a first DVT episode, researchers say. This strategy can exclude DVT in more patients without increasing missed diagnoses, according to a randomized, multicenter, controlled trial in 1723 patients at five medical centers in Canada.

Dr Lori-Ann Linkins (McMaster University, Hamilton, ON) and colleagues published their findings in the January 15, 2013 issue of the Annals of Internal Medicine.

D-dimer testing is sensitive but not specific for identifying DVT, Linkins et al note. "In this trial comparing uniform with selective D-dimer testing in patients with suspected first DVT, a selective strategy—which used a higher D-dimer threshold to exclude first acute DVT in outpatients with low C-PTP and omitted D-dimer testing in outpatients with high C-PTP and all inpatients—was as safe as and more efficient than the uniform testing strategy, which used the same threshold to exclude DVT in all patients," the authors write.

Patients were randomly assigned to selective testing (n=860) or uniform testing (n=863) after presenting to the hospital with a suspected first DVT episode. In the selective group, D-dimer testing was used in patients with a low or moderate C-PTP of having a DVT, while no D-dimer test was used in patients with a high C-PTP (these patients were sent directly for venous ultrasonography). A cut point of >0.5 µg/mL was used to define patients with a high likelihood of having a DVT. Investigators then looked to see whether the more selective use of D-dimer testing might translate into more venous thromboembolisms (VTEs) three months down the road.

"You're not missing cases"

VTE was diagnosed during follow-up in just four patients: 0.8% of the 506 D-dimer-positive patients with normal initial ultrasonogram and 0.5% of the 798 patients without DVT on initial testing who were still in the study at three-month follow-up. No outpatients with low C-PTP and D-dimer levels between 0.5 and 1.0 µg/mL were diagnosed with VTE during follow-up, and no VTE was diagnosed during follow-up in any D-dimer-negative patient.

As well, of the 72 D-dimer-positive patients, eight (11%) had DVT diagnosed by ultrasonography during initial testing. No patient with a normal ultrasonogram experienced VTE during follow-up.

There was no difference between the selective- and uniform-testing groups in the number of VTE events over the follow-up period.

Overall, selectively testing D-dimer levels lowered the proportion of patients who needed ultrasonography by 7.6% and decreased the percentage of patients who required D-dimer testing by 21.8%, the authors concluded.

In an interview, Dr Dani el J Giaccio (Lutheran Medical Center, Brooklyn, NY), commenting on the study, stressed the importance of reducing the need for ultrasounds, as demonstrated by the selective testing strategy.

"In this day and age of cost-effectiveness, and especially with the incentives . . . for doctors to practice more cost-effective care, [it's good] to know that you're not missing cases—you're actually picking up more," he explained.

The study was supported by a grant from the Heart and Stroke Foundation of Ontario . L inkins has disclosed no relevant financial relationships. Disclosures for the coauthors are listed on the journal's website . Giaccio has disclosed no relevant financial relationships .

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