Evaluation of 24-Hour D-Dimer Stability at Room Temperature

Abstract Objective To determine the stability of plasma D-dimer after 24 hours of storage at room temperature (23–25°C). Methods In this paired ex vivo study, citrated plasma from 365 oncology patients was analyzed at baseline (HemosIL D-Dimer HS 500 on an ACL TOP 550) and again after 24 hours of room-temperature storage in capped microtubes. Agreement was assessed with the Wilcoxon signed-rank test, Passing–Bablok regression, percentage-difference Bland–Altman analysis, and diagnostic concordance at 500 ng/mL fibrinogen equivalent units (FEU) (0.50 mg/L FEU). Results Median D-dimer was 292 ng/mL FEU at baseline and 294 ng/mL FEU at 24 hours ( P = .70). Passing–Bablok regression showed no constant or proportional bias. The mean relative bias was − 1.6% (95% limits of agreement, − 45.4% to 42.3%), with the largest differences at low concentrations. Diagnostic concordance was 95.9% (350/365; κ = 0.90), but 12 of 108 baseline-positive samples (11.1%) became negative after storage. Conclusions Plasma D-dimer showed high overall stability after 24 hours at room temperature, suggesting that laboratories can process delayed samples. Borderline-positive results should be interpreted cautiously because of a small risk of false-negative classification.