Kaiser Permanente research supports the use of cystatin C tests as an alternative to creatinine-based tests for accurately assessing kidney function without taking race into account.The study was published on the same day that a joint task force of the National Kidney Foundation and the American Society of Nephrology (NKF-ASN) urged the immediate adoption of race-free eGFR equations.
In a related press release, Kaiser Permanente researchers stated that their findings may inform future NKF-ASN guideline recommendations on the evaluation of kidney function.Test for cystatin C in the blood vs. creatinine in the blood“Our research demonstrated that if you use a blood cystatin C test instead of a blood creatinine test, you don’t need to include race to get a similarly accurate estimate of kidney function,” Alan S. Go, MD, a senior research scientist at the Kaiser Permanente division of research in Northern California, said in a press release.Chi-yuan Hsu, MD, a nephrologist at the University of California, San Francisco and an adjunct investigator with the Kaiser Permanente Division of Research, and co-lead author of the study, stated, “Cystatin C solves the scientific problem of maintaining comparable accuracy and it achieves the social and scientific goal of eliminating the need to consider race.
”Researchers examined data from 1,248 adults with chronic kidney disease to investigate methods for estimating GFR without taking race into account. Race as reported by the participant, genetic ancestry markers, serum creatinine, serum cystatin C, and 24-hour urinary creatinine levels were all evaluated.
Three alternatives to current GFR estimations were considered by the researchers.“First, we investigated whether we could replace race in GFR estimation with a quantitative measure of genetic ancestry.
Second, we tested whether we could replace race in GFR estimation by accounting for serum creatinine determinants that are unrelated to GFR and vary by race. Third, we investigated whether we could eliminate the need to consider race – and genetic ancestry, based on the results of our first set of analyses – in GFR estimation by replacing serum creatinine with serum cystatin C as the glomerular filtration marker,” the researchers wrote.
When using current formulations of GFR estimating equations in participants who identified as Black, the results showed that a model that omitted race resulted in more underestimation of GFR (median difference between measured and estimated GFR was 3.99 mL per minute per 1.73 m2 of body-surface area) and lower accuracy compared to models that included race (median difference was 1.11 mL per minute per 1.73 m2).Similarly, researchers discovered that incorporating genetic ancestry data instead of race resulted in greater GFR underestimation and lower accuracy than models that included race (median difference was 1.33 mL per minute per 1.73 m2).
“Inclusion of non-GFR determinants of serum creatinine level (eg, body-composition metrics and urinary excretion of creatinine) that differed based on race reported by participants and genetic ancestry did not eliminate the misclassification introduced by removing race (or ancestry) from serum creatinine-based GFR estimating equations,” the researchers wrote.Race and genetic ancestry are not required.When estimating GFR with cystatin C, however, findings revealed that incorporating race or genetic ancestry was not required to achieve “similarly statistically unbiased and accurate estimates in Black participants” (median difference was 0.33 mL per minute per 1.73 m2).
“Our findings show that race and genetic ancestry are linked to a person’s creatinine level, and we can’t get around that even when we account for a wide range of other factors, such as muscle mass, dietary protein intake, and other factors that are thought to influence blood creatinine level independent of kidney function,” Go said. “We believe that switching to the cystatin C test will promote greater equity for people of all races and ethnicities.”The NKF-ASN task force’s most recent recommendations suggest that all laboratories in the United States begin using the CKD-epidemiology collaboration creatinine equation without including race, as well as increasing the use of cystatin C and combining creatinine and cystatin C markers to obtain more accurate assessments of kidney function.
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