Quality of serum creatinine measurement in light of EQA programs

Background: The aim of our study was to identify the role of External Quality Assessment (EQA) programs in improving the quality of serum creatinine measurement and glomerular filtration rate (GFR) estimation. Comparison of results achieved during EQA with National Kidney Disease Education Program and College of American Pathologists guidelines identified an urgent need for an improvement in measurement quality. We compared actual results for serum creatinine measurement within the Czech Republic EQA with the requirements of EC Directive 98/79. Methods: We used the results for 2005-2006 EQA programs. There were seven surveys involved with two samples each, and a 2006 questionnaire on the post-analytical phase survey. Results: Bias depended strongly on the creatinine concentration. However, this dependence varied for different in vitro diagnostic manufacturers, although they should all follow the same directive. We chose biological variation as the significance rate for bias and a resulting overall error of 6.9%. The proportion of results with total error < 6.9% ranged from 11% to 80%. The total error for a reference sample of 94.8 mu mol/L also showed significant dependence on the working calibrator used and ranged from 1% to 17%. Conclusions: The main role of EQA programs in improving the quality of creatinine measurement results and GFR calculation should be in monitoring the quality of IVD products, enabling users to adapt their use of these products accordingly. EQA programs can also educate on performing GFR estimation in a unified way. Highly commutable control materials with certified creatinine values or, alternatively, lyophilized materials with sufficient commutability proved by comparison with native frozen human sera, should become an important EQA tool.