There is known variability in reported results for measurement of cystatin C among and even within a single IVD manufacturer’s cystatin C measurement procedure. Consequently, the calculated eGFR values using these cystatin C measured concentrations also show variability. To minimize this variability, the International Federation for Clinical Chemistry and Laboratory Medicine (IFCC) Working Group on Standardization of Cystatin C prepared an international reference material (Grubb et al. Clin Chem Lab Med 2010).
This reference material is distributed by the European Joint Research Institute for Reference materials and Measurements (JRC-IRMM) in Geil, Belgium as certified reference material ERM-DA471/IFCC (http://irmm.jrc.ec.europa.eu/ ) and first became available to manufacturers of cystatin C reagents and clinical laboratories in late 2010. The primary goal of this working group was to provide a high-level reference material that could be used by manufactures or clinical laboratories to help improve the accuracy and reduce the laboratory-to-laboratory variability of reported cystatin C measurements and thereby greatly enhance the accuracy of eGFR that laboratories report using cystatin C-based equations (Grubb A, Blirup-Jensen S, Lindström V et alClin Chem Lab Med. 2010; 48:1619-21.
Users of cystatin C measurements for clinical or research purposes should also be aware of drift in Cysatin C assays. This has been well documented in the Siemens assay. We documented a drift of approximately 13% downward in the Siemens assay between 2003 and 2009 at the University of Minnesota and other laboratories have communicated similar drifts. At the University of Minnesota, the Siemens assay is 12% lower than reference methods (Stevens AJKD 2011).
Last Updated: July 2014