Objectives: D-dimer testing is an important component of the workup for pulmonary embolism (PE). However, age-related increases in D-dimer concentrations result in false positives in older adults, leading to potentially unnecessary imaging utilization. The objective of this study was to quantify the test characteristics of an age-adjusted D-dimer cut-off for ruling out PE in older patients investigated in actual clinical practice.
Methods: This observational study used administrative data from four emergency departments from July 2013 to January 2015. Eligible patients were ages 50 and older with symptoms of PE who underwent D-dimer testing. The primary outcome was 30-day diagnosis of PE, confirmed by imaging reports. Test characteristics of the D-dimer assay were calculated using the standard reference value (500 ng/ml), the local reference value (470 ng/ml), and an age-adjusted threshold (10 ng/ml × patient’s age).
Results: This cohort includes 6,655 patients ages 50 and older undergoing D-dimer testing for a possible PE. Of these, 246 (3.7%) were diagnosed with PE. Age-adjusted D-dimer cut-offs were more specific than standard cut-offs (75.4% v. 63.8%) but less sensitive (90.3% v. 97.2%). The false-negative risk in this population was 0.49% using age-adjusted D-dimer cut-offs compared with 0.15% with traditional cut-offs.
Conclusion: Age-adjusted D-dimer cut-offs are substantially more specific than traditional cut-offs and may reduce CT utilization among older patients with suspected PE. We observed a loss of sensitivity, with an increased risk of false-negatives, using age-adjusted cut-offs. We encourage further evaluation of the safety and accuracy of age-adjusted D-dimer cut-offs in actual clinical practice.
Keywords: administrative data; pulmonary embolism; venous thromboembolism.