The CKD-EPI Equation for Estimating GFR from Serum Creatinine

The Cockcroft-Gault equation was published in 1976 and was widely adopted for estimation of creatinine clearance from serum creatinine levels (1). The equation was developed using two steps: First, urinary creatinine excretion per body weight (UV/kg) was estimated from age in hospitalized patients; creatinine clearance was then calculated by multiplying by weight and dividing by serum creatinine (P) using the standard “UV/P” clearance formula. Not surprising, the high-risk patients who were used to develop the Cockcroft-Gault equation had lower muscle mass (creatinine excretion) than healthier individuals in the general population (2). The lack of a standardized serum creatinine assay has also been considered a problem with the Cockcroft-Gault equation, but this is not the case. Serum creatinine assay calibration has no influence on the coefficients of the Cockcroft-Gault equation, because the regression did not involve serum creatinine. Because the Cockcroft-Gault equation was developed using only white men, however, the model was not optimized to account for gender and race differences in muscle mass. Nonetheless, the Cockcroft-Gault equation is still used widely, particularly for drug dosing, for which estimates in ml/min units are desired. Because the Cockcroft-Gault equation has been used to determine recommended dosages for various medications (3), there is a consistent approach when using this equation to adjust medication dosage. However, the clinician should keep in mind that many dosing recommendations were made prior to serum creatinine standardization.By contrast, the most widely used GFR-estimating equation today is the Modification of Diet in Renal Disease (MDRD) equation, which was published in 1999 and later simplified (4,5). This equation automatically estimates GFR from serum creatinine for most laboratories (6). This equation was developed using patients who who had CKD identified …