Abstract
Abstract Background: Chronic kidney disease (CKD) and acute kidney injury (AKI) affect over 850 million individuals worldwide, with diagnosis and management heavily dependent on laboratory biomarkers. Reliable assessment of kidney biomarkers is therefore essential. External Quality Assessment (EQA) plays a critical role in ensuring the accuracy and comparability of results across laboratories. Methods: We retrospectively analyzed EQA data from a Brazilian proficiency testing provider (January 2009–March 2024). Reported results for serum creatinine, urinary creatinine, urinary albumin, and total urinary proteins were evaluated. Coefficients of variation (CVs) and adequacy percentages (%Adequacy) were compared across methods using the Kruskal–Wallis test. Trends were assessed with the Mann–Kendall test. Results: For serum and urinary creatinine, amidinohydrolase/oxidase methods consistently showed the lowest CVs (~3–4.5%) compared with Jaffé-based methods. For urinary albumin, turbidimetry demonstrated superior performance (~5.0% CV), while for total urinary proteins, benzethonium chloride methods yielded the best results (~5.0% CV). Across all biomarkers, CVs decreased and %Adequacy increased significantly over the 15-year period, particularly at clinically relevant concentrations. Nevertheless, Jaffé-based creatinine methods remained predominant despite their well-documented specificity limitations. Conclusion: Over 15 years, participant laboratories improved the precision and adequacy of kidney biomarker measurements in EQA programs. However, persistent reliance on outdated Jaffé-based creatinine methods compromises standardization and clinical reliability. Adoption of more specific methods and participation in clinically relevant EQA programs are essential to further strengthen laboratory quality and patient safety.