Exclusion of acute pulmonary embolism: computed tomography pulmonary angiogram or D-dimer?

Eng CW, Wansaicheong G, Goh SKJ, Earnest A, Sum C
Correspondence: Dr Eng Chee Way, engcheeway@yahoo.com.sg

ABSTRACT
Introduction The aim of our study was to determine the accuracy of the D-dimer test in the exclusion of pulmonary embolism.
Methods In 2006, 446 patients at our hospital underwent computed tomography pulmonary angiogram (CTPA) for the exclusion of pulmonary embolism. We selected patients with a clinical suspicion of pulmonary embolism, and who underwent both a CTPA examination and a D-dimer test performed within a period of five days. Pregnant women, patients with an allergy to intravenous contrast and those who were on anticoagulant therapy were excluded. Based on our criteria, 219 cases were selected. D-dimer test was performed using an immunoturbidimetric assay. A cut-off value of 500 ng/ml was selected as the upper limit to exclude thrombosis.
Results There were 42 patients positive for pulmonary embolism on CTPA and all had elevated D-dimer values. There were 177 patients negative for pulmonary embolism on CTPA and 49 of them had normal D-dimer values. The sensitivity and specificity of the D-dimer test was 100.0 percent (95 percent confidence interval [CI] 91.6–100.0) and 27.7 percent (95 percent CI 21.2–34.9), respectively. The likelihood ratio for a positive test and negative test was 1.38 and 0, respectively.
Conclusion The D-dimer test is suitable for screening patients with a clinical suspicion of pulmonary embolism. The indiscriminate use of CTPA results in unnecessary testing and elevates healthcare costs. Clinicians are urged to give due consideration to a D-dimer test result prior to requesting a CTPA examination.

Keywords: computed tomography pulmonary angiogram, D-dimer, pulmonary angiogram, pulmonary embolism
Singapore Med J 2009; 50(4): 403-406