Method Comparison of PT, INR, and aPTT Results Obtained Using Two Coagulation Analyzers in Routine Laboratory Practice.

Background/Objectives: Prothrombin time (PT), international normalized ratio (INR), and activated partial thromboplastin time (aPTT) are routinely used coagulation assays, and analyzer-reagent differences may affect result comparability. This study evaluated analytical comparability between the Sysmex CS-2500 System using Siemens reagents and the Tokra Medical NOVAE II for PT, INR, and aPTT. Methods: Residual routine citrated plasma specimens were measured on both systems. The CS-2500 was designated as the comparator system. Passing-Bablok regression and Bland-Altman analysis were used as the primary method-comparison approaches; Pearson and Spearman correlations and exploratory categorical agreement were secondary analyses. Results: Fifty paired measurements were analyzed for PT and INR and 54 for aPTT. For all three parameters, the 95% confidence interval (CI) for the Passing-Bablok intercept included 0 and the 95% CI for the slope included 1, providing no statistically supported evidence of constant or proportional bias by regression. Mean paired differences (NOVAE II minus CS-2500) were +1.27 s for PT, +0.023 for INR, and +2.32 s for aPTT. The 95% limits of agreement were -0.15 to +2.69 s for PT, -0.112 to +0.159 for INR, and -1.70 to +6.33 s for aPTT. Categorical agreement was influenced by analyzer-specific reference intervals and by the low prevalence of abnormal results. Conclusions: The two analyzer-reagent systems showed positive analytical associations, but the magnitude and dispersion of paired differences varied by assay. Because no clinical equivalence margins were prespecified and markedly pathological or therapeutic-range samples were sparsely represented, these findings support analytical comparison and local verification but do not establish clinical interchangeability.