Study finds creatinine-based eGFR equation could reduce racial differences in transplant waitlist times

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In light of recent shifts away from race-based algorithms in medicine—such as the adjustment for Black race in equations that estimate patients’ kidney function—new research published in the Clinical Journal of the American Society of Nephrology (CJASN) has examined the impact use of these new equations could have on kidney transplant waitlist access between Black and white patients.

“We believe that the findings in our study are helpful in providing some preliminary data on how use of the different GFR [glomerular filtration rate]-estimating equations would theoretically affect wait-time accrual prior to the start of dialysis,” said first author Elaine Ku (University of California, San Francisco, USA).

Current methods primarily rely on measuring kidney function from a patient’s serum creatinine levels via their estimated GFR (eGFR). Historically, eGFR equations included an adjustment for Black versus non-Black race, resulting in higher eGFR values for Black versus non-Black patients. But—recognising that race is a social construct rather than a biological phenomenon—a joint taskforce led by the American Society of Nephrology (ASN) and the US National Kidney Foundation (NKF) endorsed the removal of race modifiers from kidney function estimations by publishing a new set of race-free GFR equations last year.

EGFR is the primary criterion for determining eligibility for registration on the kidney transplant waitlist in patients not yet treated with dialysis—a concept dubbed ‘pre-emptive waitlisting’. Pre-emptive wait-time accrual, or the waiting time that can accumulate before a patient starts dialysis, impacts when a patient may ultimately be offered a kidney transplant. According to current national policy in the USA, patients can begin to accrue wait time for transplantation when their eGFR is 20mL/min or less.

In their CJASN paper, Ku and colleagues report that they examined the use of two race-free 2021 Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equations and whether they could minimise racial differences in accruable pre-emptive waitlist times. The team determined the association between race (Black or white) and time spent with eGFR<20mL/min per 1.73m2 that could potentially be accrued as pre-emptive wait time, using a new race-free, creatinine-based equation, and another race-free equation that uses blood levels of cystatin C as an indicator of kidney function. Their retrospective cohort study involved chronic renal insufficiency cohort (CRIC) participants who were theoretically eligible for waitlist registration.

Across 472 eligible CRIC participants, the researchers found that, with the new race-free, creatinine-based equation, time to kidney failure was similar between Black and white patients, meaning potential pre-emptive wait times were also similar for Black versus white patients—with a median wait time that could be accrued of 23 months for Black patients and 22 months for white patients.

However, across 441 eligible participants, the time to kidney failure for Black patients using the cystatin C-based, race-free equation was shorter, leading to a potential wait time that was 20% shorter for Black patients versus white counterparts. The median wait time that could be accrued for Black patients was 21 months compared to 26 months for white patients and, via a ’bootstrapping’ analysis method, Ku and colleagues determined a statistically significant difference between the time ratios of the models using the creatinine-based equation and the cystatin C-based alternative.

“We found that the new creatinine-based equation seemed to be associated with a 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,” Ku noted.

These results build on a previous study, also conducted by Ku and her colleagues, showing that Black patients had a shorter time to kidney failure (theoretically accruing less wait time) when the older, Black race-adjusted equation was used.

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