. Author manuscript; available in PMC: 2015 May 6.

Published in final edited form as: Am J Kidney Dis. 2011 Aug 19;58(4):682–684. doi: 10.1053/j.ajkd.2011.05.019

Table 1.

List of equations

Steps in standardization of cystatin C
Equation 1	Scys-UMN'09= 0.083 + 0.789 ^* Scys-CCRL'03
Equation 2	standardized Scys = 1.12 ^* Scys-UMN'09
Equation 3^*	standardized Scys = 0.093 + 0.884 ^* Scys-CCRL'03
Equation 4^**	Scys-CCRL'03= −0.105 + 1.13 ^* standardized Scys
CKD-EPI equations for non-standardized Scys
Equation 5	eGFR = 76.7 ^* (Scys)⁻¹¹⁹
Equation 6	eGFR = 127.7 ^* (Scys)⁻¹¹⁷ ^* age⁻⁰¹³ ^* (0.91 if female) ^* (1.06 if black)
Equation 7	eGFR = 177.6 ^* standardized Scr^−0.65 ^* (Scys)^−0.57 ^* age^−0.20 ^* (0.82 if female) ^* (1.11 if black)
CKD-EPI equations re-expressed for standardized Scys^{^}
Equation 8	eGFR = 76.7 ^* (−0.105 + 1.13 ^* standardized Scys)^−1.19
Equation 9	eGFR = 127.7 ^* (−0.105 + 1.13 ^* standardized Scys)^−1.17 ^* age^−0.13 ^* (0.91 if female) ^* (1.06 if black)
Equation 10	eGFR = 177.6 ^* standardized Scr^−0.65 ^* (−0.105 + 1.13 ^* standardized Scys)⁻⁰ ⁵⁷ ^* age^−0.20 ^* (0.82 if female) ^* (1.11 if black)

UMN, University of Minnesota; CCRL, Cleveland Clinic Research laboratory; ScysC, serum cystatin C; Scr, serum creatinine

Combination of equation 1 and 2

^**

Re-expression of equation 3

^{^}

Cystatin C assays traceable to the reference materials produced and characterized from the International Federation for Clinical Chemists (IFCC) Working Group for the standardization of Scys and the Institute for Reference Materials and Measurements (IRMM). The reference material was produced by adding recombinant cystatin C into a serum pool from blood donors, with the assigned value established by dry mass analysis.

Standardized serum creatinine (standardized Scr), refers to creatinine measured with assays that are traceable to the certified reference materials for creatinine whose value was assigned using isotope dilution mass spectroscopy.