Evaluation of analytical reliability based on variance index score, measurement uncertainty and root cause analysis in a 2-year external quality assessment scheme

Objectives: To evaluate analytical performance in a clinical biochemistry laboratory using an integrated approach combining variance index score (VIS), measurement uncertainty (MU), target score and root cause analysis (RCA) based on external quality assessment scheme (EQAS) data. Materials and Methods: This retrospective analytical study evaluated EQAS results generated over 2 years (January 2022 to December 2023) in a National Accreditation Board for Testing and Calibration Laboratories-accredited tertiary-care clinical biochemistry laboratory. A total of 1,853 EQAS results covering 68 analytical parameters were analysed across multiple platforms and programmes, including Bio-Rad EQAS, Randox International Quality Assessment Scheme and the Quality Assurance Forum. Analytical performance was assessed using VIS, target score for immunoassays, MU estimated by the Nordtest top-down approach and structured RCA for EQAS outliers. Statistical analysis: Descriptive statistics were applied. VIS, target score and MU were expressed as means with minimum and maximum values. EQAS outliers were reported as counts and percentages, and RCA findings were categorised by phase of error. Results: Of the 1,853 EQAS results analysed, 96.4% were within acceptable limits. Sixty-seven outliers (3.61%) were identified. Most deviations originated in the analytical phase (79.1%), followed by pre-analytical causes, while no post-analytical errors were observed. Routine chemistry, electrolyte and immunoassay parameters demonstrated predominantly good to excellent VIS and MU performance. Parathyroid hormone showed persistently high VIS and MU values, indicating analytical bias. Conclusions: The synthesis of VISs, MU, target scores and structured RCA offers a comprehensive framework for evaluating EQAS. Integrating these quality indicators streamlines the identification of analytical deviations, guides targeted corrective and preventive interventions and reinforces analytical reliability and continuous quality improvement within clinical biochemistry laboratories.