Discrepancies between two D-dimer assays and impact on clinical decisions; a retrospective analysis of samples tested in community and hospital-based laboratories in Auckland.

AIM: In patients with suspected venous thromboembolism, an elevated D-dimer level provides an important branch-point in the management pathway. This study compared two D-dimer assays, INNOVANCE® DDimer (Innovance) and STA®-Liatest® D-Di Plus (Liatest), to assess potential impact on clinical management. METHOD: Reflecting current practice in Waitemata, Auckland, we compared paired samples from 805 patients referred to hospital following a community D-dimer test. Samples were determined to be positive or negative using a 500µg/L fibrinogen equivalent units (FEU), and age-adjusted cut-offs. RESULTS: In the Innovance assay, 2% of samples had a result <500µg/L FEU. In contrast, by Liatest, 18% were below 500µg/L. This positive bias of Innovance was amplified with use of age-adjusted cut-offs; 23% of samples with an elevated Innovance result showed a normal result by Liatest. On average, the Innovance values were 22% higher than Liatest. Results suggestive of interference from heterophile antibodies were seen in 6% of sample-pairs. CONCLUSION: Innovance D-dimer test yielded higher values than Liatest and experienced interference from suspected heterophile antibodies. Discrepancies in nearly a quarter of patients may be leading to substantial under or over investigation, inefficient use of resources and clinical confusion.