Final report on EURAMET.QM-K12: EURAMET key comparison on the determination of the mass fraction of creatinine in serum

Abstract

Creatinine is a well-known marker for the evaluation of kidney function. Its routine measurement is undertaken by many clinical laboratories and comparable results over distance and time are required for effective diagnosis. To address this need many National Measurement Institutes (or designated institutes) provide services in this area via the provision of higher order standards or reference measurements. The organic analysis working group of the consultative committee for amount of substance have conducted two previous key comparisons to assess the equivalence of institutes who provide such services. The purpose of this study was to enable institutes who missed the previous studies to demonstrate their capability for characterizing serum materials containing 1 µg/g to 100 µg/g of creatinine.The study material consisted of two lyophilized serum samples which were used in an external quality control proficiency testing scheme. No target values were available for these materials and all participants reported results within the one month timeframe given for analysis. Five institutes participated in the key study and a single institute submitted results for the parallel pilot study. All participants in the key study used isotope dilution with either gas or liquid chromatography coupled with mass spectrometry. The pilot study laboratory used a novel isotope dilution surface-enhanced Raman spectroscopy method.The comparison reference value for each material was set as the mean of all results submitted by those participating in the key study. The choice of the reference value estimator was constrained as it was deemed more appropriate to treat the data in a similar manner to CCQM-K12 if the relative degrees of equivalence were to be compared. This resulted in reference values of (54.27 ± 0.72) µg/g and (38.01 ± 0.42) µg/g for the two separate materials. The relative degrees of equivalence were calculated and these were compared with the relative degrees of equivalence of participants in CCQM-K12. The range of participants' results in EURAMET.QM-K12 for both levels (2% and 3% respectively for materials A and B) was greater than the 1% achieved in CCQM-K12. However, it was concluded that this study was suitable to support CMCs for creatinine in serum for 1 µg/g to 100 µg/g with uncertainties at the 1% to 1.5% level. This was found to be fit for purpose and consistent with the majority of CMCs currently approved.Main text.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).