CKD-EPI Cystatin C Equation (2012)

eGFR =
133 x
min(S_cys/0.8, 1)^-0.499 x
max (S_cys/0.8, 1)^-1.328 x
0.996^Age x
0.932 [if female]

Abbreviations / Units

eGFR (estimated glomerular filtration rate) = mL/min/1.73 m²

S_cys (standardized serum cystatin C) = mg/l

min = indicates the minimum of S_cys/0.8 or 1

max = indicates the maximum of S_cys/0.8 or 1

age = years

Assays

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.

Clinical Use

Can be used as a confirmatory test for the diagnosis of chronic kidney disease in patients with a decreased GFR as estimated from creatinine.
Data suggests that 3.6% of U.S. adults would be classified as having CKD solely on the basis of a creatinine-based GFR estimate of 45 to 59 ml per minute per 1.73 m². A strategy of measuring cystatin C when the creatinine-based estimate is in this range and then reestimating GFR with the use of both these markers could correctly reclassify a substantial proportion of such patients as not having chronic kidney disease and not being at high risk.
Can also be used to screen for CKD among persons who have a creatinine-based GFR estimate of 60 to 74 ml per minute per 1.73 m² without albuminuria (10.9% of U.S. adults) or to obtain a more accurate estimation of GFR in patients with muscle wasting or chronic illness.

References

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, Schmid CH, Tighiouart H, et al. Estimating glomerular filtration rate from serum creatinine and cystatin C. N Engl J Med. 2012;367(1):20-29.
Peralta CA, Shlipak MG, Judd S, et al. Detection of chronic kidney disease with creatinine, cystatin C, and urine albumin-to-creatinine ratio and association with progression to end-stage renal disease and mortality. JAMA 2011;305:1545-52.
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;22:147-55.
Stevens LA, Padala S, Levey AS. Advances in glomerular filtration rate-estimating equations. Curr Opin Nephrol Hypertens. 2010;19:298-307.