Clinical approaches to managing venous thromboembolism (VTE) have changed measurably over the last decade, giving clinical laboratories a new and integral role in helping providers manage VTE patients. The Journal of Applied Laboratory Medicine (JALM) addressed this issue in depth, discussing the latest VTE guidelines in a review, editorial, and podcast.
VTE, which includes deep venous thrombosis (DVT) and pulmonary embolism (PE) is responsible for thousands of deaths in the United States each year, with cases expected to double over the next 30 years. Best practices for screening, diagnosing, and managing this disease have been the center of much debate, wrote Rugvedita S. Parakh, MBBS and Daniel E. Sabath, MD, PhD, authors of the JALM review. Using recommendations by the American College of Chest Physicians as a backdrop, the authors discussed screening, diagnosis, thromboprophylaxis, and management techniques for DVT and PE.
Clinicians are overutilizing thrombophilia testing, the authors stressed. The test can produce false-positive or false-negative results if a patient is having an acute VTE episode or undergoing regular anticoagulant treatments. There is a dearth of guidelines or recommendations on screening for thrombophilia, and several studies have questioned the test’s clinical utility. One clinical audit of thrombophilia testing in children with acute thromboembolic events “elucidated potential harms of thrombophilia testing (namely, unnecessary blood draw and estimated annual single-institution cost of $82,000) without affecting clinical management and recommended that this testing should be avoided in acute settings,” according to Parakh and Sabath.
Thrombophilia testing rarely changes clinical management, which is moving in the direction of treating patients based on VTE cause and risk of recurrence, Sabath, hematology division head of the University of Washington School of Medicine’s laboratory medicine department, told CLN Stat. “In general, in the setting of provoked thrombosis, treatment will be limited to three months or so. In the case of unprovoked thrombosis, patients may get extended treatment, and this will be independent of whether or not a lab tests says they have a clotting tendency,” he said.
Creating a lab formulary in which laboratories and providers agree on which tests are permitted and under what circumstances, is the best way to prevent unnecessary testing, Sabath said.
A D-dimer test can rule out disease in low to moderate risk patients in the acute setting, whereas lupus anticoagulant and antiphospholipid antibody testing can help identify VTE causes in acute care. “For longer term management of VTE, testing for inherited thrombotic tendency is often pursued but may be of limited clinical utility,” wrote Parakh and Sabath.
D-dimer tests aren’t without their challenges, however, stressed Karen A. Moser, MD, in a related editorial. Although useful in helping to exclude VTE patients with low pretest probability, the positive predictive value in these assays is weak, “meaning that a positive D-dimer result cannot by itself confirm a diagnosis of VTE,” she wrote. Imaging studies such as ultrasound for DVT and computed tomography pulmonary angiography for PE are usually required to definitively diagnose VTE.
A wide variety of D-dimer kits are commercially available, but some aren’t sufficiently sensitive enough to exclude VTE, Moser continued. Clinical labs need to understand the differences among these tests and whether they’ve been cleared to aid in VTE diagnosis or exclude it. Another challenge is there’s no standardization for these tests. “The numerous D-dimer assays commercially available at present use a variety of different monoclonal antibodies with specificity for different epitopes on D-dimer, leading to interassay variation,” observed Moser, who recommended that labs advocate for standardization efforts and clearer guidance from medical literature regarding these tests.
According to Sabath, labs should be able to provide a sensitive D-dimer assay with a reasonably quick turnaround time. “It is important to make sure the units are specified so that providers can understand the significance of the results compared to what is described in the literature,” he said.
More from JALM is available online about screening, diagnosing, and treating VTE conditions.