Background Creatinine measurement for estimation of glomerular filtration rate (GFR) is a frequently used laboratory test. Differences in analytic creatinine methods have caused large inter-laboratory variation. International and national standardization efforts have been made in the last decade. Methods This study describes the results of the standardization efforts in Sweden by summarizing data for creatinine concentration in blood plasma in the Equalis quality assessment program during 1996-2014. Results Non-compensated Jaffe methods dominated in 1996-2001 (91 of 103 laboratories; 90%) and were then gradually replaced by either compensated Jaffe methods or enzymatic creatinine methods. In 2014 a majority of Swedish hospital laboratories (139 of 159; 87%) used enzymatic methods. The reported mean creatinine value by the Swedish laboratories was about 10 μmol/L higher than the isotope dilution mass spectrometry (IDMS) assured reference value in 2003, but consistent with the reference value from 2009 to 2014. The inter-laboratory CV was 7%-9% for creatinine values until 2007, and thereafter gradually decreased to about 4%-5% in 2014. Conclusions The introduction of enzymatic methods in Swedish laboratories has contributed to achieving a low inter-laboratory variation. Also, the reported values are lower for enzymatic methods compared to Jaffe methods, and the values obtained with enzymatic methods were consistent with IDMS certified values established at reference laboratories. Thus, many Swedish hospital laboratories reported 10 μmol/L lower, and more true, creatinine concentrations in 2012 than in 2003, which may cause bias in longitudinal studies.
Keywords: creatinine methods; external quality assessment; harmonization; inter-laboratory variation; standardization.