Evaluation of the impact of standardization process on the quality of serum creatinine determination in Italian laboratories

Background: Creatinine determination in serum is a key indicator of kidney glomerular function. A reference measurement system for its standardization is available and virtually all IVD manufacturers have aligned their assays to this system. In this study, we verified the impact of these standardization efforts on the results of an Italian EQAS involving about 430 laboratories. Method: We considered data obtained during 2006, 2010 and 2011 schemes of EQAS Prolarit for control materials with target values assigned by a traceable method (enzymatic assay calibrated against the NISI' SRM 967). Results: The results showed a good alignment at concentrations similar to 170 mu mol/L, with 2011 results - except for one method group - well inside the desirable bias (+/- 4%). At higher concentrations, whereas the bias was small in 2010, for some groups using alkaline-picrate (AP) methods it became significantly negative in 2011. The performance seems to worsen when measuring physiologic concentrations, where a significant positive bias (up to similar to 20%) is shown by most of the AP-based analytical systems. With few exceptions, no evident improvement in individual assay bias was noted from pre- (2006) to post-standardization (2011) periods. The enzymatic method groups were the only always presenting an acceptable bias at all creatinine concentrations, also showing the lowest between-laboratory variability. Conclusion: Our data seem to indicate that the standardization efforts are still having effects lower than expected. Even taking into consideration that some of the bias may derive from non commutability problems, most of the current standardized AP-based methods, at the lower creatinine concentrations, seem to present accuracy problems. This inaccuracy can adversely impact the estimation of GFR by equations and the evaluation of kidney function in pediatrics. (C) 2013 Elsevier B.V. All rights reserved.