How Might Eliminating Race-based Adjustments in Kidney Function Estimates Affect Kidney Transplant Waitlisting?

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Recognizing that race is a social and not a biological construct, several health care institutions no longer report patients’ kidney function through estimated glomerular filtration rate (eGFR) equations that have an adjustment for Black race. ASN and the National Kidney Foundation have endorsed this move, and a new set of race-free equations to estimate GFR was published in 2021.

New research published in CJASN (1) examines the impact of using these new equations on kidney transplant waitlist access.

The study looked specifically at how the new equations will affect when patients not yet treated with dialysis can begin to accrue wait time for transplantation—or preemptive waitlisting. eGFR is the primary criterion for determining eligibility for registration on the kidney transplant waitlist in these patients, and preemptive wait time accrual—or the waiting time that can accumulate before a patient starts dialysis—affects when a patient may ultimately receive an offer for a kidney transplant. According to current national policy, patients can begin to accrue wait time for transplantation when their eGFR is <20 mL/min/1.73 m².

Previously, the study's investigators showed that when using the older equation that included Black race, individuals of Black race had a shorter time to kidney failure (and would theoretically accrue less wait time). In the current research, the investigators wondered whether using new race-free equations to guide preemptive waitlisting would minimize racial differences in accruable preemptive wait time. The team determined the association between race (Black or White) and time spent with eGFR <20 mL/min/1.73 m² using the new race-free, creatinine-based equation or a new race-free, cystatin C-based equation.

When using the new race-free, creatinine-based equation, time to kidney failure was similar between patients of Black and White race; however, the time to kidney failure was still shorter for patients of Black race using the cystatin C-based, race-free equation.

The results suggest that using the race-free, creatinine-based equation to determine preemptive waitlist eligibility is the strategy that may reduce racial differences in access to preemptive wait time accrual.

“We believe that the findings in our study are helpful in providing some preliminary data on how use of the different GFR estimating equations would theoretically affect wait time accrual prior to the start of dialysis,” said lead author Elaine Ku, MD, MAS, of the University of California, San Francisco. “We found that the new creatinine-based equation seemed to be associated with more similar wait time that could potentially be accrued compared with use of the cystatin C-based equation, but our findings require further validation in larger groups of patients.”

…[I]t is uncertain what consequences there may be from widespread implementation of this formula.

An accompanying editorial by Rhiannon D. Reed, DrPH, and Jayme E. Locke, MD, MPH, FACS, FAST (2), both of the University of Alabama at Birmingham, notes that although a race-free, creatinine-based equation for eGFR may attenuate racial differences in access to kidney transplantation, it is uncertain what consequences there may be from widespread implementation of this formula.

“While the number of Blacks affected by use of the new formula will be smallest for dialysis initiation and referral for transplantation, more Blacks will be affected at higher eGFR thresholds, including kidney donor candidacy and post-donation follow-up. There would be a corresponding increase in the prevalence of chronic kidney disease among individuals in the general population who identify as Black and may now be excluded from kidney donation, thus limiting access to living donation in a population already at a disadvantage,” the authors wrote. “There are also potential implications for enrollment and conduct of clinical trials, such as fewer outcomes observed in trials where events are more likely to occur in those with lower eGFR who may now be excluded. Furthermore, while systematic overestimation among non-Blacks has the potential to result in inappropriate drug continuation or overdosing for medications, underestimation among Blacks may result in drug discontinuation and underdosing, including chemotherapeutic agents and weight loss medications.”