Modern Medical Laboratory Journal

Introduction: C-peptide measurement is an essential tool in the assessment of endogenous insulin secretion and in the management of diabetes. However, differences in analytical methods between platforms may impact result comparability. This study aims to evaluate the agreement between two commonly used automated immunoassays for C-peptide quantification: Alinity® (Abbott) and Cobas e411® (Roche Diagnostics).
Material and Methods: A total of 100 serum samples were randomly selected from routine C-peptide tests. Internal quality controls were performed daily on both analyzers, prior to each C-peptide assay run, on the same day. Statistical analyses were carried out using MedCalc® software (version 23.1.7).
Results: The two methods showed good correlation (r² = 0.9907). Bland-Altman analysis revealed a mean bias of −6.61% between the two analyzers, indicating that Alinity® tends to provide slightly lower values compared to Cobas e411®. The Passing-Bablok regression equation obtained was: y (Alinity®) = −0.154 + 0.989 × x (Cobas e411®).
Discussion and Conclusion: Although both methods demonstrated strong correlation and satisfactory linearity across the entire concentration range, the observed systematic difference may have clinical implications, particularly in patient monitoring or interpretation of C-peptide–derived indices. These findings highlight the importance of standardization and harmonization of assay methods to ensure optimal comparability between analytical platforms.