Establishing biological variation for plasma D-dimer from 25 healthy individuals.

D-dimer is considered to be a reliable marker of both coagulation activation and fibrinolysis. However, data on biological variation (BV) of D-dimer is still limited, causing the use of empiric analytical performance specifications and lack of other implications related to BV. This study aimed to estimate the BV of plasma D-dimer employing a study design compliant with The Biological Variation Data Critical Appraisal Checklist. Blood samples were collected from a cohort of 25 healthy subjects (16 females, 9 males; age range, 19-61 years) from Turkey once weekly for 3 consecutive weeks. All plasma samples were analyzed in duplicate within a single run on Roche Cobas c501. The results were assessed for outliers, variance homogeneity, normal distribution, and trend, followed by nested ANOVA to determine BV and analytical variation estimates with confidence intervals (CIs). Gender stratified BV estimates were also calculated. Within-subject (CV) and between-subject (CV) BV estimates with 95% CIs were for D-dimer 21.2% (17.8-25.9) and 30.9% (21.3-46.2), respectively. No significant BV differences were observed between females and males. The index of individuality (II) and the reference change value (RCV) were calculated as 0.71 and 60.4%, respectively. Analytical performance specifications for desirable imprecision, bias, and total error were 10.6, 9.4, and 26.8%, respectively. This study provides well-characterized BV estimates for D-dimer, which may be helpful for setting objectively analytical performance specifications. Moreover, RCV should be preferred to decide whether a significant difference is present between serial D-dimer measurements from an individual.