Determination of the production rate and non-renal clearance of cystatin C and estimation of the glomerular filtration rate from the serum concentration of cystatin C in humans.

Cystatin C has been proposed as an endogenous marker for measuring glomerular filtration rate (GFR) and is regarded as being equivalent to or better than creatinine. However, there are no published data on the production rate (Cyspr) or on the non‐renal clearance of cystatin C (CLnr) in humans, which are essential parameters for GFR calculation. GFR was determined by measuring the plasma clearance of iohexol. Cystatin C, creatinine, urea and albumin were determined on the same serum samples as iohexol; 381 patients with a GFR range of 12–151 ml/min/1.73 m2, and 70 patients on haemodialysis were evaluated. Renal clearance of cystatin C (CLr) equals GFR * S (the sieving coefficient). Plasma clearance (CL) = CLr+CLnr. The relationship between Cyspr and the elimination rate (CL * serum‐cystatin C) can be expressed as Cyspr = (S * GFR+CLnr) * serum‐cystatin C. Assuming that the unknown values of Cyspr and CLnr are independent of GFR, the equation can be solved from GFR (iohexol clearance) and serum cystatin C ...