D-Dimer and CT Rule Out Pulmonary Embolism

Inclusion of ultrasonography of the leg did not alter 3-month thromboembolic events in a large group of patients with suspected pulmonary embolism, compared with those assessed with a D-dimer test and multislice CT only, according to a randomized, multicenter study.

“We believe that our findings can be applied to a broad population with suspected pulmonary embolism, and that [the findings] lend support to the hypothesis that a negative MSCT [multislice CT] or ELISA [enzyme-linked immunosorbent assay] D-dimer measurement safely excludes pulmonary embolism in patients with a low or intermediate clinical probability of pulmonary embolism,” Dr. Marc Righini, an internist in the division of angiography and hemostasis at Geneva University Hospital, and his associates wrote.

They assessed 1,819 consecutive outpatients with a suspected pulmonary embolism who presented to the emergency department at one of six medical centers in Europe from January 2005 to August 2006. The prevalence of pulmonary embolism was 20.6%. Men made up about 45% of the study population, mean age was 59 years, and about 18% had a history of venous thromboembolism.

After exclusions, 855 patients were randomized to undergo double testing with a serum D-dimer assay and MSCT imaging. Another 838 patients had a triple assessment with serum D-dimer, venous compression ultrasonography of the leg, and MSCT.

The primary outcome was the risk of venous thromboembolism events at 3 months in patients who, because of the diagnostic tests' results, were not treated for pulmonary embolism. The thromboembolic risk at follow-up was 0.3% in the double-testing group (2 patients of 673 with complete follow-up) and 0.3% in the triple-testing group (2 patients of 686), thus indicating noninferiority of the double-testing strategy.

“Our results show that ultrasound is no longer required as a safety net for the identification of clots that might have been missed by MSCT,” the authors wrote (Lancet 2008;371:1343–52).

The dual strategy was 24% less expensive than the triple-testing protocol, according to a comparison of mean diagnostic test cost per patient. “Therefore, our data do not support the routine use of ultrasound,” they wrote. They added that ultrasound would allow avoidance of MSCT in only 1 of every 11 patients.