November 27, 2019 -- A new way to interpret blood test results in patients examined for blood clots in the lungs has shown that a higher than usual D-dimer level can rule out pulmonary embolism, according to research published November 27 in the New England Journal of Medicine.
The new approach, developed by researchers at McMaster University in Hamilton, Ontario, Canada, and Hamilton Health Sciences, a hospital network in Hamilton, is helpful with D-dimer blood tests, which physicians utilize when trying to rule out the presence of a blood clot.
The researchers determined that a higher than usual D-dimer level can be considered a negative result, indicating that no blood clot exists, if the physician already assessed the patient as having a low probability of having a pulmonary embolism.
The approach could have a significant impact due to fewer patients needing computed tomography (CT) scans, enabling them to avoid unnecessary exposure to radiation and spend less time in the emergency department.
"Our analyses show that pulmonary embolism is ruled out by a D-dimer level of less than 1,000 ng/mL in patients with a low probability, and by a D-dimer level of less than 500 ng/mL in patients with a moderate probability," said first author Dr. Clive Kearon, PhD, a professor of medicine at McMaster University and a thrombosis specialist with Hamilton Health Sciences. "This way of using D-dimer testing and clinical assessment reduced the need for CT scanning by one-third."
The investigators enrolled and evaluated 2,017 patients ages 18 and older in their study. Of these, 7% had a pulmonary embolism upon initial diagnostic testing. The average age of the patients was 52 years; 66% were female.
Of the patients in the study, 1,474 (73%) were enrolled at Hamilton Health Sciences or St. Joseph's Healthcare Hamilton. These patients and those at other university-based clinical centers in Canada were tested from December 2015 through May 2018. They were also assessed 90 days afterward.
In total, 1,325 patients were identified by an emergency department physician as having a low (1,285 of the patients) or moderate (40 patients) probability of pulmonary embolism and had negative D-dimer results -- less than 1,000 ng/mL or 500 ng/mL, respectively. None of these patients had venous thromboembolism during follow-up examinations.
"The primary goal of diagnostic testing for pulmonary embolism is to identify which patients should be treated with anticoagulant agents and which should not," Kearon said. "When a physician is concerned that pulmonary embolism 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."