Blood Test Can Cut Unnecessary Ultrasounds to Rule Out Blood Clots

D-dimer (DD) testing is still underutilized for the assessment of deep venous thrombosis (DVT), according to a study published in the July issue of the Annals of Vascular Surgery. Further, DD testing in conjunction with a clinical assessment to attest the likelihood of disease can significantly reduce the number of unnecessary, immediate venous duplex ultrasounds (VDUs) performed to rule out DVT.

DD is part of a degraded protein produced during the clotting process. While not specific for location, etiology, or pathology, DD can serve as a clinically sensitive marker of acute thrombotic events, including DVT, with results available in under 30 minutes. Yet, many clinicians still proceed directly to VDU, regardless of the pretest likelihood of disease or DD results to inform decision making.

The researchers retrospectively analyzed data from 1,670 patients who presented to a high-volume tertiary care center with lower limb swelling with or without associated pain during June and July of four consecutive years (2012 to 2015). Electronic health records were analyzed to collect the necessary data elements (e.g., calf or leg swelling, paralysis or bedridden, localized tenderness, previous DVT) in order to calculate the Wells criteria probability (WCP) score, assessing the pretest likelihood of DVT. Based on the WCP, patients were divided into low-, moderate-, and high-risk categories. Similarly, DD values (Siemens Innovance DD assay) categorized patients into low (0.1 to 0.59), moderate (0.60 to 1.2), and high (more than 1.3 mg/L fibrinogen equivalent units). VDU diagnosis of DVT was noted to be either proximal (above popliteal vein) or distal (below popliteal vein).

DD testing was ordered in 202 patients and correlated with all positive and negative DVT patients (100 percent sensitivity and negative predictive value, with 14.9 percent specificity and 15.9 percent positive predictive value). For the 22 patients with DD in the normal range, all were negative for DVT. However, the DVT rate was significantly increased in patients with DD levels in the moderate and high ranges.

For the 51 patients with mid-level DD results, only 3 DVTs were recorded, all of which were distal DVTs.

"There is little doubt that using a combination of WCP and DD, along with establishing new thresholds or cut points for DD levels by receiver operator characteristic curve analysis, WCP, or age adjustment, can help compensate

for the low specificity of DD alone," write the authors led by Albeir Mousa, M.D., from West Virginia University in Charleston.

Unnecessary VDUs were conducted on the 685 patients with low WCP probability and no DD testing, plus the 77 patients with low or intermediate DD, yielding a total of 762 patients that had an unnecessary immediate VDU study, the authors say.

The authors estimate that at $1,557 per imaging study (minus the cost of DD testing at $182/test), there was a total of $1,047,75 in potential charge savings.

"With current constraints of health resources, better utilization of DD as an integral part of diagnostic workup for VTE is imperative," the authors conclude.

Takeaway: Higher utilization of DD testing in the workup of patients with suspected DVT can limit unnecessary VDU imaging and yield substantial health care savings.