Blood concentration of cystatin C is independent of muscle mass and tubular secretion. It can be used, in the absence of a reference method, as an alternative marker to creatinine for the evaluation of renal function and the estimation of glomerular filtration rate (GFR). Both particle-enhanced immunonephelemetry (PENIA) or immunoturbidimetry (PETIA) methods are available to determine cystatin C. From an analytical point of view, it is recommended to use methods whose calibration is traceable to the reference material (ERM-DA471/IFCC) and to report an estimated GFR based on cystatin C. The main equations used are those developed in 2012 by the group "Chronic kidney disease epidemiology collaboration (CKD-EPI)" for adults and those published by Schwartz in 2012 for children. National and international recommendations suggest using a cystatin C-based GFR estimate as a confirmatory test in the clinical settings where the relationship between creatinine production and muscular mass impairs the clinical performance of creatinine. The indications retained by the working group were graded according to the level of recommendations. The essential indications are the estimation and/or the monitoring of renal function in children and adolescents due to rapid changes in muscle mass; in patients with impaired muscle mass and in patients with an alteration of tubular secretion of creatinine (essentially iatrogenic effects).
Keywords: cystatin C; estimation; glomerular filtration rate; indications; recommendations.