Specificity of quantitative latex agglutination assay for D-dimer in exclusion of pulmonary embolism in the emergency department.

We assessed the prevalence of elevated quantitative latex agglutination assay for D-dimer in patients in the emergency department in whom pulmonary embolism (PE) was excluded. D-dimer was normal (<230 ng/mL) in 435 (83%) of the 522 patients. D-dimer was normal in 88% of the patients with musculoskeletal or related chest pain, 74% with pleurisy or pleuritic chest pain, and 85% with upper respiratory tract infection. D-dimer was 230 to 500 ng/mL in 65 (75%) of the 87 in whom D-dimer was elevated. Clinical probability was low in 31 (48%) of the 65 patients with D-dimer levels of 230 to 500 ng/mL. D-dimer was 230 to 500 ng/mL and clinical probability was low in 31 (36%) of the 87 patients who had computed tomographic (CT) angiograms because of elevated D-dimer. Negative likelihood ratio for PE is sufficiently low that PE can be excluded with reasonable certainty in such patients. Tailoring cutoff value to 500 ng/mL in patients with low clinical probability would have reduced CT angiograms by 36%.