To diagnose kidney disease, physicians calculate estimated glomerular filtration rate, or eGFR, as a measure of kidney function. Those calculations factor in a patient’s age, sex and levels of serum creatinine, a waste product in the bloodstream that’s filtered out by the kidneys and is detected using a standard blood test.
Following study results in 1999 that found, on average, higher levels of serum creatinine in Black patients regardless of kidney function, self-reported race has also been factored into eGFR calculations.
That practice has led to more than two decades of potential misdiagnoses because of the vast genetic diversity within the Black population, according to Afshin Parsa, M.D., program director of the National Institutes of Health’s long-running Chronic Renal Insufficiency Cohort (CRIC) study at the National Institute of Diabetes and Digestive and Kidney Diseases.
“Misdiagnosis could lead to a person receiving incorrect drug dosing, or delays in receiving dialysis or a kidney transplant,” Parsa said. “Current eGFR calculations could be exacerbating racial inequities in a disease that disproportionately affects Black people.”
In a new analysis of data collected in the CRIC study, Parsa and other researchers propose using a blood test to measure cystatin C rather than creatinine to eliminate the need to consider race in kidney disease diagnoses.
Like creatinine, cystatin C is regulated by the kidneys, so higher-than-normal levels of the protein can indicate a drop in kidney function. Unlike creatinine, however, cystatin C can be used to calculate eGFR without needing to be compounded by race data.
In the study, the researchers performed standard eGFR calculations using creatinine and cystatin C levels of nearly 1,250 patients, both with and without the addition of race and genetic ancestry data. They found that while creatinine measurements sans the race coefficient resulted in misclassifications and inaccuracies—even when a variety of other non-race data related to creatinine levels were factored in—cystatin C could be used to accurately determine eGFR without requiring self-reported race information.
Only about 31% of the estimations that used creatinine levels without including race came within 10% of actual measured GFR levels, down from the 42% that met that threshold when creatinine was adjusted according to race. Cystatin C, sans race, reached that point 41% of the time, proving its viability as a non-race-based replacement for creatinine measurements.
Plus, because the protein can be measured in the same way as creatinine—with a standard blood test—it wouldn’t be a difficult swap for healthcare providers.
“We hope this study’s results will build momentum toward widespread adoption of cystatin C for the purposes of estimating GFR. The alternative eGFR test requires no special equipment, can be standardized and the more it’s adopted, the less it would cost,” said Chi-yuan Hsu, M.D., lead author of the study.