Pulmonary Embolism Blood Tests Reduce Radiation Exposure

A new study suggests that D-dimer blood tests can help rule out pulmonary embolism (PE), reducing the need for a diagnostic computerized tomography (CT) scan.

Researchers at McMaster University (Hamilton, ON, Canada), the University of Alberta (Edmonton, Canada), McGill University (Montreal, Canada), and other institutions conducted a prospective study involving 2,017 adult (average age 52 years, 66% female), of whom 7.4% had PE on initial diagnostic testing. PE was considered to be ruled out without further testing in outpatients with a low clinical pretest probability (C-PTP) and a D-dimer level of less than 1000 ng per milliliter, or with a moderate C-PTP and a D-dimer level of less than 500 ng per milliliter.

All other suspected patients underwent chest imaging (usually CT pulmonary angiography); if PE was not diagnosed, the patients did not receive anticoagulant therapy. All patients were followed for 3 months to detect venous thromboembolism (VTE). The results revealed that none of patients who were ruled out based on C-PTP and d-dimer levels had VTE at follow-up. Of 1,863 patients who did not receive a diagnosis of PE initially, and did not receive anticoagulant therapy, one patient had VTE. The study was published on November 27, 2019, in the New England Journal of Medicine (NEJM).

“When a physician is concerned that PE may be present, chest imaging with CT pulmonary angiography is usually done in half of these patients. We wanted to find a way to reduce the number of CT scans that need to be done,” concluded lead author Professor Clive Kearon, MB, PhD, of McMaster University. “Our diagnostic strategy resulted in the use of chest imaging in 34.3% of patients, whereas a strategy in which PE is considered to be ruled out with a low C-PTP and a d-dimer level of less than 500 ng per milliliter would result in the use of chest imaging in 51.9%. This way of using D-dimer testing and clinical assessment reduced the need for CT scanning by one-third.”

D-dimer is a fibrin degradation product. It is so named because it contains two D fragments of the fibrin protein joined by a cross-link. Since its introduction in the 1990s, it has become an important test for patients with suspected thrombotic disorders. While a negative result practically rules out thrombosis, a positive result can indicate thrombosis, but does not rule out other potential causes. Its main use, therefore, is to exclude thromboembolic disease where the probability is low.

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McMaster University
University of Alberta
McGill University