Comparative Evaluation of Reagent Lot-to-Lot Variability using In-house, NABL 112 and CLSI EP26-A Protocols: A Cross-sectional Study in a Clinical Biochemistry Laboratory

Introduction: Reagent lot-to-lot variation represents a subtle yet significant source of analytical uncertainty in clinical laboratories. Even minor shifts between reagent lots can alter assay calibration, bias, and precision, thereby compromising longitudinal comparability and, ultimately, patient safety. Despite explicit requirements in the International Organisation for Standardisation (ISO) 15189:2022 and the National Accreditation Board for Testing and Calibration Laboratories (NABL) 112, verification procedures remain heterogeneous across laboratories and often rely on limited empirical evaluation rather than statistically defined acceptance criteria. Aim: To undertake a comparative assessment of reagent lotto-lot variability across seven key biochemical analytes using three verification frameworks-an in-house laboratory protocol, NABL 112, and the Clinical and Laboratory Standards Institute (CLSI) EP26-A guideline-in a NABL-accredited clinical biochemistry laboratory. Materials and Methods: The present cross-sectional study was conducted over a twelve-month period in a tertiary care, NABL-accredited laboratory in Gujarat, India. Paired patient samples and quality control materials were analysed across reagent lot transitions on Siemens analysers. Verification outcomes were evaluated using regression analysis, Total Allowable Error (TEa), Measurement Uncertainty (MU), and Critical Difference (CD) metrics, as prescribed by the respective protocols. Results: All analytes met the acceptance criteria under the in-house and NABL 112 protocols. Under the CLSI EP26-A framework, Thyroid-Stimulating Hormone (TSH) failed acceptance (observed difference=2.3 mIU/L>rejection limit (RL)=0.88 mIU/L), while all other analytes conformed. The EP26-A protocol required larger sample sizes and narrower rejection limits, demonstrating greater sensitivity in detecting clinically meaningful differences between reagent lots. Conclusion: While conventional verification protocols ensure operational efficiency, the CLSI EP26-A approach provides a statistically robust and clinically aligned framework for detecting reagent lot variability. Integrating its principles into routine practice could enhance analytical reliability, regulatory compliance, and long-term traceability of patient results within accredited laboratory systems.