What are creatinine based GFR estimating equations?
Prior to the CKD-EPI equation, there were two main creatinine equations in use: the Cockcroft-Gault and the Modification of Diet in Renal Diseases (MDRD) Study equation.
The Cockcroft-Gault formula was developed in 1973 using data from 249 hospitalized, veteran men.
The multiplier of 0.85 for females was not based on any empiric data because the initial cohort was all men, and was suggested by the author as a reasonable decrease in creatinine generation in women compared with men.
The Cockcroft-Gault formula estimates creatinine clearance rather than GFR, so it systematically overestimates GFR because of creatinine secretion. It was derived prior to creatinine standardization, which has led to lower serum values, hence it also systematically overestimates creatinine clearance.
In addition, inclusion of a term for weight in the numerator leads to systematic overestimation of creatinine clearance in patients who are edematous or obese and underestimation in those who are thin or frail, and because of the form of the function of age, it systematically underestimates creatinine clearance in the elderly.
The Cockcroft-Gault formula is less accurate than newer equations and should no longer be used.
The four-variable MDRD Study equation was developed in 1999 using data from 1628 patients with CKD with GFR from approximately 5 to 90 mL/min per 1.73 m 2 . It estimates GFR adjusted for BSA.
The equation was reexpressed in 2005 for use with a standardized serum creatinine assay (the four-variable MDRD Study equation):
The CKD-EPI equation was as accurate as the MDRD Study equation in the subgroup with estimated GFR less than 60 mL/min per 1.73 m 2 and substantially more accurate in the subgroup with estimated GFR greater than 60 mL/min per 1.73 m 2 . Thus the MDRD Study equation is no longer recommended.
More recently, other creatinine-based equations have been developed in white Europeans—the Berlin Initiative Study and the CAPA (Caucasian, Asian, pediatric, and adult) equation—and both have been shown to be equivalent to CKD-EPI in elderly whites and more biased in blacks.
Several modifications to the MDRD or CKD-EPI equations have been developed for use in regions outside of North America, Europe, and Australia.
