• All GFR estimating formulas on this site are designed for use with standardized creatinine and standardized cystatin C values.
    • Standardized creatinine values are traceable to isotope dilution mass spectrometry (IDMS).
    • Standardized cystatin C values are traceable to the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC)/Institute for Reference Materials and Measurements (IRMM) working group.
  • Your laboratory can confirm whether or not it uses standardized creatinine values traceable to IDMS, and standardized cystatin C values traceable to IFCC and IRMM.
  • All laboratories in the US and other countries should be using standardized creatinine and cystatin methods. To properly estimate GFR, the serum creatinine and cystatin C must be measured accurately. Consequently, the calculators for older, non-standardized methods of calculating GFR in adults are no longer available on this website.
  • For more information, go to or


  1. Inker LA. Frequently Asked Questions About GFR Estimates. New York: The National Kidney Foundation; 2011.
  2. Grubb A, Blirup-Jensen S, Lindstrom V, Schmidt C, Althaus H, Zegers I. First certified reference material for cystatin C in human serum ERM-DA471/IFCC. Clin Chem Lab Med. 2010;48(11):1619-1621.
  3. Kidney Disease: Improving Global Outcomes (KDIGO) CKD Work Group. KDIGO 2012 clinical practice guideline for the evaluation and management of chronic kidney disease. Kidney Int. 2013;3:1-150.