CKD-EPI Creatinine-Cystatin Equation (2021)

eGFR_cr-cys = 135 x min(S_cr/κ, 1)^α x max(S_cr/κ, 1)^-0.544 x min(S_cys/0.8, 1)^-0.323 x max(S_cys/0.8, 1)^-0.778 x 0.9961^Age x 0.963 [if female]

where:

S_cr = standardized serum creatinine in mg/dL

κ = 0.7 (females) or 0.9 (males)

α = -0.219 (female) or -0.144 (male)

min(S_cr/κ, 1) is the minimum of S_cr/κ or 1.0

max(S_cr/κ, 1) is the maximum of S_cr/κ or 1.0

S_cys = standardized serum cystatin C in mg/L

Age (years)

Assays

Creatinine is assayed using methods that are traceable to IDMS assigned NIST certified reference materials. To learn more, go to nkdep.nih.gov.
Cystatin C is assayed using methods that are traceable to IFCC and IRMM certified reference materials. To learn more, go to http://ckdepi.org/assays/cystatin-c/ or http://nkdep.nih.gov/lab-evaluation/cystatin-c.shtml.

Designed for use with standardized creatinine values that are calibrated to be IDMS traceable and standardized cystatin C values. To learn more, click here.
May provide more accuate estimates in patients with differences in diet, extremes of muscle mass (such as body builders or patients with muscle wasting), or those outside the boundaries of where the MDRD Study equation has been validated.
May also prove useful in estimating change in eGFR over time in people with changing muscle mass or diet.
May have a role in identifying persons with CKD who have the highest risk for complications.
Cystatin C is a basic protein produced by all nucleated cells. It is freely filtered by the glomerulus and reabsorbed and metabolized by tubular cells, with only small amounts excreted in the urine. It is reported to be generated at a relatively constant rate, irrespective of muscle mass.
The original formula was reexpressed in 2011 for standardized cystatin C.
Developed in 2008 by the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI).

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.
Inker LA, Eckfeldt J, Levey AS, et al. Expressing the CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) cystatin C equations for estimating GFR with standardized serum cystatin C values. Am J Kidney Dis. 2011;58(4):682-684.
Peralta CA, Katz R, Sarnak MJ, et al. Cystatin C identifies chronic kidney disease patients at higher risk for complications. J Am Soc Nephrol. 2011;22(1):147-155.
Stevens LA, Coresh J, Schmid CH, et al. Estimating GFR using serum cystatin C alone and in combination with serum creatinine: a pooled analysis of 3,418 individuals with CKD. Am J Kidney Dis. 2008;51(3):395-406.