Method Comparison of Three Automated D-Dimer Assays

Background and Objective: D-dimer results differ across analytical platforms, which may affect their clinical interpretation. This study aimed to compare the analytical agreement and threshold-based classification of three routinely used D-dimer analyzers. Methods: Of 150 consecutive residual citrated plasma specimens, 81 patient specimens with valid results on the Sysmex CS-2500, Tokra Novae MTI, and VIDAS 3 analyzers were included. Agreement was assessed using the intraclass correlation coefficient, Passing-Bablok regression, Bland-Altman analysis, and classification concordance at the fixed (500 ng/mL FEU) and age-adjusted thresholds. VIDAS 3 served solely as the comparator method. Results: Overall agreement was moderate to good; however, the platforms were not fully interchangeable. Sysmex CS-2500 and VIDAS 3 showed the closest agreement, with no significant constant or proportional bias, whereas Tokra Novae MTI exhibited significant proportional bias. Mixed classification across the three analyzers occurred in 21/81 patients (25.9%) at the fixed threshold and in 18/81 patients (22.2%) at the age-adjusted thresholds. Conclusions: Clinically relevant inter-platform differences persisted despite acceptable average agreement. Therefore, D-dimer results should not be regarded as interchangeable across analyzers, particularly near clinical decision thresholds, and platform-specific verification remains essential.