Standardization of Cystatin C: development of primary and secondary reference preparations.

A Primary Reference Preparation has been produced using pure, recombinant, Cystatin C in a solvent of 0.1 mol/L KCl. Dry mass determination of the Primary Reference Preparation resulted in a Cystatin C concentration of 5.20 g/L. Agarose-electrophoresis and SDS-electrophoresis, as well as N-terminal sequencing, verified the purity, homogeneity and identity of Cystatin C in the Primary Reference Preparation. For the Secondary Reference Preparation, a serum pool was collected and stabilized. A pilot batch was made to verify the selected procedure and spiking with the pure, recombinant Cystatin C. The final Secondary Reference Preparation is now produced (4468 vials) and ready for value assignment and further characterization.

Developments in the assessment of glomerular filtration rate.

The assessment of the glomerular filtration rate (GFR) is the most commonly used test of renal function. The accepted reference procedure employs an exogenous clearance marker whilst the most popular test is that of serum or plasma creatinine. All of these tests have limitations, although the surrogate endogenous markers are the most practical. Cystatin C, a low molecular weight protein which can be measured by light scattering immunoassay, possesses many of the attributes required of the ideal GFR marker. Data on reference ranges indicate that circulating cystatin C levels reflect the variation in GFR throughout life and the marker demonstrates a better correlation with the reference procedure than serum creatinine.