"Evaluating Laboratory Quality Indicators Through External Quality Assessment Scheme (Eqas): A Focused Analysis ON Performance Trends AND Assigned Value Shifts"

Abstract

Background:
External Quality Assessment Schemes (EQAS) play a pivotal role in evaluating the analytical accuracy and inter-laboratory comparability of clinical biochemistry laboratories. Key performance indicators such as Z-scores, Assigned Values (AVs), and Coefficients of Variation (CV%) are integral to monitoring quality, particularly in laboratories adhering to ISO 15189 standards. This study aimed to analyze laboratory performance across six consecutive EQAS cycles, with a focus on detecting analyte-specific trends and identifying deviations requiring corrective action.

Methods:
A retrospective analysis was carried out using EQAS data from December 2024 to May 2025, sourced from the proficiency testing program coordinated by Christian Medical College (CMC), Vellore. Nineteen routine biochemical analytes were evaluated. Data points included AV, Z-score, CV%, and Z-score uncertainty (u*). Z-scores were interpreted using standard thresholds: |z| ≤ 2 (acceptable), 2 < |z| ≤ 3 (warning), and |z| > 3 (unacceptable). Descriptive statistics and trend analysis were conducted using GraphPad Prism 7 statistical software.

Results:
The majority of analytes demonstrated acceptable Z-score ranges and stable AVs, indicating consistent analytical performance. However, notable exceptions included ALT (Z = 24.3, February), AST (Z = 4.15, January), ALP (Z = 3.21, May), and HDL (Z > 2.0 in December, January, and May), suggesting potential issues related to methodology, calibration, or instrumentation. While CV% values were generally within acceptable limits (<20%), persistent inter-laboratory variability was observed for Amylase, ALT, and ALP. Trend analysis further revealed repeated performance warnings for HDL and ALP across multiple cycles.

Conclusion:
Long-term EQAS trend analysis is a valuable approach for identifying and addressing analytical inconsistencies in clinical laboratories. Persistent Z-score deviations and elevated CV% in enzyme and lipid assays highlight the need for improved calibration traceability, method harmonization, and strengthened internal quality control. Integrating such evaluations into routine quality management practices enhances laboratory performance, supports ISO 15189 compliance, and ensures the reliability of diagnostic results.