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Age-adjusted D-dimer excludes pulmonary embolism and reduces unnecessary radiation exposure in older adults: retrospective study

Background Patients in whom a diagnosis of pulmonary embolism (PE) is suspected and whose D-dimers are elevated frequently require CT pulmonary angiogram (CTPA) for diagnosis. Because D-dimer rises with age, an age-adjusted D-dimer threshold may prevent unnecessary radiation exposure from CTPA in older patients. Objective To determine the efficacy and safety of implementing an age-adjusted D-dimer threshold to exclude PE. Design, settings and patients Retrospective comparison of conventional and age-adjusted D-dimer thresholds in 1000 consecutive patients who had both D-dimer and CTPA. Main outcome measures Conventional and age-adjusted D-dimer thresholds for excluding PE were <250 ng/mL and 5× age for patients older than 50 years, respectively. We defined patients as unlikely to have PE using the revised Geneva score (RGS) and two different categories of clinical risk: RGS ≤5 and RGS ≤10. Results We diagnosed PE by CTPA in 244 (24.4%) patients. 3/86 patients (3.5%) whose D-dimer was below the conventional threshold of 250 ng/mL had PE (RGS 3, 9 and 14), all of which were judged to be light clot load (group 1). 3/108 patients (2.8%) whose D-dimer lay between 250 ng/mL and the age-adjusted threshold had PE (RGS 6, 8 and 9), all of which were again judged to be light clot load (group 2). 62/108 group 2 patients with RGS ≤5 were considered unlikely to have PE as were 102/108 using the RGS clinical risk category ≤10. None of the 62 patients with RGS ≤5 had PE while 3/102 patients with RGS ≤10 had PE. 236/806 patients (29.3%) whose D-dimer was above the age-adjusted threshold had PE (group 3). Conclusions In a consecutive series of 1000 patients, an RGS ≤5 and an age-adjusted D-dimer would have led to 62 fewer CTPA at a cost of no missed PEs.