Cystatin C Measurement and Interpretation Guidelines

Laboratory Reporting Standards

Clinical laboratories should measure cystatin C using assays with calibration traceable to international standard reference materials, with precision (coefficient of variation) <2.0% and desirable bias <3.2% compared to reference methodology, as recommended by the Kidney International guideline 1
Cystatin C concentration should be rounded to the nearest 100th of a whole number when expressed as conventional units (mg/L), according to the Kidney International guideline 1
The American Journal of Transplantation recommends using particle-enhanced nephelometric immunoassay or IFCC-traceable methods for cystatin C measurement 2
Serum/plasma should be separated from red blood cells by centrifugation within 12 hours of venipuncture, as stated in the Kidney International guideline 1

Cystatin C should not be interpreted in isolation but rather used to calculate estimated GFR (eGFR) using validated equations, particularly the 2012 CKD-EPI cystatin C equation, as recommended by the American Journal of Transplantation and Kidney International guidelines 1, 3
The American Journal of Transplantation guideline suggests using cystatin C for confirmatory testing in adults with eGFRcreat 45-59 mL/min/1.73 m² without other markers of kidney damage 2
Cystatin C can be used in special populations, such as liver transplant recipients, cancer patients requiring nephrotoxic drug dosing, and class III obesity, as recommended by the American Journal of Transplantation guideline 3

Thyroid dysfunction can affect cystatin C levels independent of renal function, as reported in the American Journal of Transplantation 3