Selective strategy for D-dimer testing in DVT

By Sally Robertson, B.Sc.Jan 16 2013

Selecting certain patients for D-dimer testing appears to be a safe and more efficient way of diagnosing deep vein thrombosis (DVT) than uniformly testing all patients suspected of having the condition, report researchers.

"As currently used, D-dimer testing is sensitive but not specific for diagnosing DVT. A negative result (D-dimer level <0.5 ug/mL) excludes the diagnosis, but a positive test result (≥0.5 ug/mL) mandates additional testing, usually venous ultrasonography," explain Lori-Ann Linkins (McMaster university, Ontario, Canada) and colleagues.

By raising the D-dimer threshold used for uniform testing from 0.5 ug/mL to 1.0 ug/mL and then testing only patients with a low or moderate likelihood of having DVT, the team correctly identified the same amount of DVT as when they tested all patients, including inpatients and those with a high likelihood of having DVT.

As reported in the Annals of Internal Medicine, this revised procedure substantially reduced the number of D-dimer assays and the number of ultrasonographies required to confirm DVT.

In the randomized, multicenter, controlled trial, the researchers used the 9-point Wells clinical prediction rule to categorize the patients' clinical pretest probability (C-PTP) for DVT as low, moderate, or high.

They found that using the D-dimer threshold of 1.0 µg/mL to exclude DVT in outpatients with low C-PTP halved the number requiring ultrasonography compared with testing uniformly at the lower D-dimer threshold, at 72 (20%) of 360 patients versus 137 (41%) of 334 patients, respectively.

Furthermore, none of the patients with D-dimer levels between 0.5 and 1.0 ug/mL (88 selective, 81 uniform) were diagnosed with symptomatic venous thromboembolism during initial testing or over a 3-month follow-up period, confirming the safety of this approach, says the team.

The selective testing strategy also improved efficiency over uniform testing by omitting D-dimer testing in outpatients with high C-PTP and in all inpatients who were due to have ultrasonography as a matter of course. Only 15% of outpatients with high C-PTP and 2% of inpatients in the uniform group had DVT excluded by a negative result on D-dimer testing.

"To our knowledge, this trial is the first to point toward selective D-dimer testing as a safe and efficient testing strategy in patients with suspected first DVT," say the researchers.

"Future studies to determine whether this diagnostic strategy can be applied to patients who present with suspected recurrent DVT or PE [pulmonary embolism] are required," they conclude.

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