Patient Care

Negative D-Dimer Test Can Safely Exclude Pulmonary Embolism in Patients at Low To Intermediate Clinical Risk


Clinical question: In patients with symptoms consistent with pulmonary embolism (PE), can evaluation with a clinical risk assessment tool and D-dimer assay identify patients who do not require CT angiography to exclude PE?

Background: D-dimer is a highly sensitive but nonspecific marker of VTE, and studies suggest that VTE can be ruled out without further imaging in patients with low clinical probability of disease and a negative D-dimer test. Nevertheless, this practice has not been adopted uniformly, and CT angiography (CTA) overuse continues.

Study design: Prospective registry cohort.

Setting: A 550-bed community teaching hospital in Chicago.

Synopsis: Consecutive patients presenting to the ED with symptoms suggestive of PE were evaluated with 1) revised Geneva score; 2) D-dimer assay; and 3) CTA. Among the 627 patients who underwent all three components of the evaluation, 44.8% were identified as low probability for PE by revised Geneva score, 52.6% as intermediate probability, and 2.6% as high probability. The overall prevalence of PE (using CTA as the gold standard) was very low (4.5%); just 2.1% of low-risk, 5.2% of intermediate-risk, and 31.2% of high-risk patients were ultimately found to have PE on CTA.

Using a cutoff of 1.2 mg/L, the D-dimer assay accurately detected all low- to intermediate-probability patients with PE (sensitivity and negative predictive value of 100%). One patient in the high probability group did have a PE, even though the patient had a D-dimer value <1.2 mg/L (sensitivity and NPV both 80%). Had diagnostic testing stopped after a negative D-dimer result in the low- to intermediate-probability patients, 172 CTAs (27%) would have been avoided.

Bottom line: In a low-prevalence cohort, no pulmonary emboli were identified by CTA in any patient with a low to intermediate clinical risk assessment and a negative quantitative D-dimer assay result.

Citation: Gupta RT, Kakarla RK, Kirshenbaum KJ, Tapson VF. D-dimers and efficacy of clinical risk estimation algorithms: sensitivity in evaluation of acute pulmonary embolism. AJR Am J Roentgenol. 2009;193(2):425-430.

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