For 20 years, race, a social interpretation of how one looks, has been a core component of leading equations used to calculate estimated glomerular filtration rate (eGFR). These equations were meant to replace the Cockcroft-Gault (CG) equation, a race-neutral approach that used age, sex, and weight to estimate creatinine clearance. The first widely used eGFR equation—the Modification of Diet in Renal Disease (MDRD) study equation—was introduced to replace the CG equation because the latter was criticized for not incorporating body surface area indexing. The assumption was that Black individuals have higher serum creatinine with the same level of kidney function as Whites because on average they have more muscle mass. Even if this is biologically plausible, it was wrong to use racial profiling as a surrogate for higher muscle mass. The CKD-EPI equation that followed a decade later kept the race index in the eGFR calculation. There is now little doubt that both the MDRD and CKD-EPI equations have contributed to structural racism in medicine and public health.
How health care providers embraced these race-based equations for 2 decades is unclear. These equations resulted in eGFR values 16% to 21% higher for Black patients than White patients. Patients have continued to receive differential treatments because of their race. Black patients of the same age and sex as White patients and who had the same serum creatinine concentration would not be waitlisted for kidney transplantation because their eGFR values would be higher than the expected threshold for waitlisting eligibility. If this is not structural racism, then what is it?
The lesson from this experience is that we should be careful before discrediting well-established methods for estimating kidney function and replacing them with new ones. We should never allow race or other social constructs such as sexual orientation or place of birth to be used for any type of profiling. Clinical pharmacists, to their credit, have never given up using the CG equation for drug dosing. Recently, some colleagues who were also involved with the creation of the MDRD and CKD-EPI equations in the past rushed to introduce a new race-neutral eGFR equation based on data from studies of several thousand people. So far, I have decided not to use it. Rather, I use the current equations without the race index: the CG equation that has a weight adjustor, and increasingly, cystatin C-based equations that are inherently race-neutral.
Let us never forget that race is a social construct that should have no place in addressing biologic variability in anything, including kidney function or muscle mass.
Kam Kalantar-Zadeh, MD, PhD, MPH
Professor & Chief, Division of Nephrology, Hypertension & Kidney Transplantation
UC Irvine School of Medicine, Orange, CA