Cystatin C is recognized as a useful marker for kidney damage. Several equations have been developed to estimate eGFR from serum cystatin C. Because cystatin C measurement procedures do not produce uniform results, the estimating equations are restricted for use only with results from the specific method used to develop them. Consequently, there is a need to standardize cystatin C calibration to enable more widespread use of eGFR estimating equations that use cystatin C concentration in the calculation.
The International Federation of Clinical Chemistry and Laboratory Medicine/Institute for Reference Materials and Measurements working group for standardization of cystatin C (WG-SCC 8.3.37) has produced a primary reference preparation of isolated human cystatin C, characterized it and determined its concentration by dry mass analysis. It has also produced and distributed into about 4000 vials a secondary reference preparation of stabilized human serum to which isolated human cystatin C has been added. Protocols have been established for value transfer from the first to the secondary reference preparation using three different immunochemical procedures. The value transfer process is currently underway. The date for release of the secondary reference preparation with a stated cystatin C concentration value (= the international calibrator) is not determined, but the release is expected to occur during 2009. Questions concerning the standardization process can be directed to anders.grubb@med.lu.se. It is possible to be notified as soon as the international calibrator is released by communicating this wish in an e-mail to jrc-irmm-rm-sales@ec.europa.eu.
References
Blirup-Jensen S, Grubb A, Lindström V, Schmidt C, Althaus H: Standardization of cystatin C: Development of primary and secondary reference preparations. Scand J Clin Lab Invest 68: Suppl. 241, 67-70 (2008)
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