Performance of age‐adjusted D‐dimer cut‐off to rule out pulmonary embolism

Summary: Background: Age‐adjusted D‐dimer cut‐off has recently been proposed to increase D‐dimer usefulness in older patients suspected of pulmonary embolism (PE). Objective: We externally validated this age‐adjusted D‐dimer cut‐off using different D‐dimer assays in a multicenter sample of emergency department patients. Methods: Secondary analysis of three prospectively collected databases (two European, one American) of patients suspected of having PE. D‐dimer performance for ruling out PE was assessed by calculating negative likelihood ratio (nLR) for D‐dimer with age‐adjusted D‐dimer cut‐off (< age × 10 in patients over 50 years) and with conventional cut‐off (< 500 μg dL^?1). Test efficiency was assessed by the number needed to test (NNT) to rule out PE in one patient. Results: Among 4537 patients included, overall PE prevalence was 10.1%. In the overall population, nLR was 0.06 (95% confidence interval, 0.03–0.09) with conventional cut‐off and 0.08 (0.05–0.12) with age‐adjusted cut‐off. Using age‐adjusted cut‐off, nLR was 0.08, 0.09 and 0.06 for Vidas^®, Liatest^® and MDA^® assays, respectively. Use of age‐adjusted cut‐off produced a favorable effect on NNT in the elderly; the greatest decrease was observed in patients > 75 years: NTT halved from 8.1 to 3.6. The proportion of patients over 75 years with normal D‐dimer was doubled (27.9% vs. 12.3%). Conclusions: Our study shows that age‐adjusted D‐dimer had low nLR, allowing its use as a rule‐out PE strategy in non‐high pretest clinical probability patients, as well as using Vidas^®, Liatest^® or MDA^® assays. This age‐adjusted cut‐off increased clinical usefulness of D‐dimer in older patients. A large prospective study is required to confirm these results.