Clinical usefulness and safety of an age-adjusted D-dimer cutoff levels to exclude pulmonary embolism: a retrospective analysis

Age-adjusted D-dimer (AADD) appears to increase the proportion of patients in whom pulmonary embolism (PE) can safely be excluded compared with conventional D-dimer (CDD), according to a limited number of studies. The aim if this study was to assess whether the use of an AADD might safely increase the clinical usefulness of CDD for the diagnosis of PE in our setting. Three hundred and sixty two consecutive outpatients with clinically suspected PE in whom plasma samples were obtained to measure D-dimer were included in this post hoc analysis of a previous study. CDD cutoff value was 500 ng/mL and AADD was calculated as (patient's age x 10) ng/mL in patients aged > 50. Sensitivity, specificity, clinical usefulness (i.e., proportion of true-negative tests among all patients with suspected PE), and the proportion of false negatives were calculated for both AADD and CDD among patients with low-to-moderate clinical probability of PE according to Well's criteria. PE was confirmed in 98 patients (27 %). Among 331 patients with low-to-moderate clinical probability of PE, sensitivity and clinical usefulness were 100 and 27.8 % for CDD, respectively, and 100 and 36.5 % for AADD, respectively. In 29 patients aged > 50 with CDD > 500 ng/mL, AADD showed values under its normal cutoff point, without false negatives for the diagnosis of PE (0 %, 95 % CI 0-11 %). AADD increases clinical usefulness notably with respect to that of CDD in patients with clinical suspected PE without losing sensitivity in our cohort. The use of AADD apparently does not reduce the safety of CDD for the exclusion of PE.