Calibration
From 15th August 2010 the Gentian cystatin C immunoassay is calibrated against the new cystatin C World Standard reference material ERM-DA471/IFCC
The arrival of the new cystatin C World Standard is a major event in the acceptance of cystatin C as the fastest and most reliable immunoassay for assessing kidney function and measuring GFR.
Q. What is the significance of the new World Standard reference material ERM-DA471/IFCC?
A. Different cystatin C immunoassays calibrated against the World Standard reference material ERM-DA471/IFCC should give the same results. Therefore the World Standard is the standard that all cystatin C immunoassays must meet - if they are to give a true measurement of cystatin C and cystatin C estimated GFR.
Q. Is the Gentian cystatin C immunoassay changed as a result of calibration against the new World Standard?
A. No! The Gentian cystatin C immunoassay is unchanged, but we have made a tiny adjustment to the Gentian calibrator material.
Q. Does the change Gentian has made to their calibrator material have any significance for patient measurements made before and after the change?
A. No! The change to the Gentian calibrator material is insignificant. In fact, operator variability is likely to be more significant than the Gentian adjustment.
Q. Is the Gentian cystatin C equation changed?
A. No! There are no changes to the Gentian cystatin C equation so users do not have to make any changes to their procedures or calculations.
Q. Are all other cystatin C immunoassays calibrated against the new World Standard?
A. No! Calibration against the World Standard is a guarantee that the Gentian cystatin C immunoassay gives a true measurement of cystatin C and cystatin C estimated GFR.
Q. A new World Standard is an important event, how can I know if my current cystatin C immunoassay is calibrated against the new World Standard?
A. Ring your supplier and ask him to send you confirmation that your assay is calibrated against the new World Standard. If he cannot confirm your request then you should change to a brand that meets the World Standard.
Q. Why haven’t other assay producers yet calibrated against the new World Standard?
A. Some producers must re-work their assays to calibrate against the new World Standard and this can be a long and complicated process.
Q. Why is Gentian the first cystatin C immunoassay to be calibrated against the new World Standard?
A. Gentian has focused on high quality and accuracy since the Gentian cystatin C immunoassay was released in 2006. This focus means that changes to the assay were not required and the only change was a small adjustment to calibrator materials.
Q. Has Gentian been involved in the development of the new World Standard?
A. No, Gentian has not been directly involved in the development of the new World Standard. However, the Gentian cystatin C immunoassay is one of the 3 methods selected to establish the new World Standard.
Q. Where can I read more about the new cystatin C World Standard?
A. The following links are useful in understanding the importance of the new World Standard and the long process required to develop a new World Standard.
News from NKDEP (National Kidney Disease Education Program) in US
Cystatin C Standardization (Update as of July 2010).
Short Communication from Clinical Chemistry and Laboratory Medicine Journal 2010
First certified reference material for cystatin C in human serum ERM-DA471/IFCC.
Minutes from NKDEP Laboratory Working Group in US. Meeting Minutes – Manufacturers' Forum July 28, 2010. Section 5.
5. Cystatin C Standardization, Anders Grubb (Chair, IFCC WG-SCC), Lund University, Sweden.
A method for establishing calibration traceability for routine methods to a human serum based reference material:
Blirup-Jensen S, Johnson AM, Larsen M. Protein standardization V:
Value transfer. A practical protocol for the assignment of serum protein values from a reference material to a target material.
Clin Chem Lab Med 2008;46:1470-9.
