Measuring estimated GFR using a equation, such as the Modification of Diet in Renal Disease (MDRD) or Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) formula, is a more accurate assessment of kidney function than serum creatinine alone (KDIGO, 2012). The MDRD Study equation includes age, sex, and race to account for the average difference in muscle mass among subgroups in estimating GFR (Levey, et. al., 2006). IDMS-traceable MDRD Study Equation eGFR = 175 x (Standardized )-1.154 x (age)-0.203 x (0.742 if female) x (1.212 if African American) (Levey, et. al., 2006).
The CKD-EPI creatinine equation is base on the same four variables as the MDRD Study equation but uses a 2-slope spline to model the relationship between estimated GFR and serum creatinine and a different relationship age, sex and race (Levey, et. al., 2009).
CKD-EPI Equation GFR = 141 × min ( /κ, 1)α × max( /κ, 1)-1.209 × 0.993Age × 1.018 [if female] × 1.159] where: Scr is serum creatinine in mg/dL, κ is 0.7 for females and 0.9 for males, α is -0.329 for females and -0.411 for males, min indicates the minimum of Scr /κ or 1, and max indicates the maximum of Scr /κ or 1. (Levey, et. al., 2009).
The creatinine-cystatin C equation estimates GFR by confirmation testing using plasma cystatin C levels that earlier than plasma creatinine (KDIGO, 2012).
KDIGO. (2012). 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 Suppl. 2013;3:1-150.
Levey, A.S., Coresh, J., Greene, T., Stevens, L.A., Yaping, Z., Hendriksen, B.A., …& Van Lente, F. (2006). Using standardized serum creatinine values in the modification of diet in renal disease study equation for estimating glomerular filtration rate. Ann Intern Med, 145 (4), 247-54.
Levey A.S., Stevens, L.A., Schmid, C.H., Yaping, Z., Castro, A.F., Feldman, H.I., …& Coresh, J. (2009). A new equation to estimate glomerular filtration rate. Ann Intern Med, 150, 604-612.