GFR, or glomerular filtration rate, is a measure of how well your kidneys filter waste from your blood. For years, the standard equations used to estimate GFR included a race-based adjustment that automatically gave Black patients a higher kidney function score, sometimes masking the true severity of their kidney disease. In 2021, a national task force recommended removing that adjustment, and U.S. medical practice has largely shifted to a race-neutral formula.
How GFR Is Estimated
Doctors rarely measure GFR directly. Instead, they estimate it using a blood test that checks your creatinine level (a waste product your muscles produce) along with your age and sex. The result, called eGFR, is reported as milliliters per minute per 1.73 square meters of body surface area. A normal eGFR is above 90, and values below 60 sustained over three months generally indicate chronic kidney disease.
Two major equations have been used to calculate eGFR: the MDRD equation and the CKD-EPI equation. Both originally included a race variable that multiplied the result upward for patients identified as Black or African American. The MDRD equation increased eGFR by roughly 21% for Black patients, and the CKD-EPI equation increased it by about 16%.
Why Race Was Included in the First Place
The race adjustment was based on population-level data showing that, on average, Black individuals had higher creatinine levels than white individuals. Researchers attributed this to differences in muscle mass. The multiplier was meant to account for that difference so the equation wouldn’t overdiagnose kidney disease in Black patients.
The problem was that race is a social category, not a biological one. Muscle mass varies enormously between individuals regardless of race, and applying a blanket correction based on skin color produced inaccurate results for many patients. A Black patient with lower muscle mass, for instance, could receive an artificially inflated eGFR that made their kidneys look healthier than they actually were.
How the Race Adjustment Harmed Black Patients
Because the race multiplier pushed eGFR numbers higher, it systematically underestimated the severity of kidney disease in Black patients. This had real consequences at every stage of care. Patients were referred to kidney specialists later, received protective medications later, and qualified for transplant waitlists later. Many treatment decisions in kidney care hinge on specific eGFR thresholds: whether to adjust diabetes medications, when to start dialysis planning, and when a patient becomes eligible for a kidney transplant.
Kidney transplant eligibility is one of the starkest examples. Patients typically join the transplant waitlist when their eGFR drops below a certain level. With the race adjustment inflating their numbers, Black patients could reach the same true level of kidney failure as white patients but appear healthier on paper, delaying their placement on the list. A study of 126 Black transplant candidates found that 60% qualified for waitlist time corrections after the formula changed, gaining a median of 570 days (about 1.6 years) per patient. Within six months of receiving that additional credited time, 34% of those patients received a transplant.
Medication access was also affected. Several diabetes drugs require dose adjustments or must be stopped entirely when kidney function declines past a threshold. Under the old race-adjusted formula, some Black patients appeared to have enough kidney function to continue medications that should have been adjusted, while others were kept on drugs they should have been transitioned off of. Simulations comparing the old and new equations found that roughly 1 to 2% of Black patients had their eligibility for certain kidney-protective diabetes medications change when the race variable was removed.
The 2021 Shift to a Race-Neutral Formula
In 2021, the National Kidney Foundation and the American Society of Nephrology jointly recommended that all U.S. laboratories immediately adopt a new version of the CKD-EPI creatinine equation that does not include race. The task force concluded that race should not be used as a proxy for biology in kidney function testing. The new equation was developed using a diverse patient population and performs acceptably across racial groups without a separate multiplier.
The shift had significant implications for disease classification. Removing race from the equation is projected to newly identify about 434,000 Black adults with chronic kidney disease who were previously undiagnosed. Another 584,000 Black adults already diagnosed would be reclassified to a more advanced stage, making them eligible for treatments and referrals sooner. On the other side, the formula is expected to remove CKD diagnoses from about 5.5 million white and non-Black adults whose kidney function was being slightly underestimated, and reclassify another 4.6 million to less severe stages.
For transplant care specifically, the United Network for Organ Sharing prohibited the use of race-based eGFR calculations starting July 27, 2022. Transplant programs were required to review their Black candidates’ records and adjust waitlist times accordingly by January 3, 2024.
Cystatin C as a Confirmatory Test
The 2021 task force also recommended increased use of cystatin C, a different blood marker for kidney function. Unlike creatinine, cystatin C levels are not significantly influenced by muscle mass, diet, or race. An eGFR calculated from cystatin C does not require any race variable at all.
Current guidelines suggest using cystatin C to confirm a diagnosis when a creatinine-based eGFR falls below 60 but there are no other signs of kidney damage, such as protein in the urine. In these borderline cases, adding cystatin C to the calculation can meaningfully reclassify patients, either confirming that kidney disease is present or revealing that the creatinine-based estimate was misleading. The combined equation using both creatinine and cystatin C is considered the most accurate approach currently available.
What This Means for Your Lab Results
If you are a Black patient looking at older lab work, your eGFR may have been calculated with the race adjustment, meaning your kidney function was likely reported as higher than it truly was. Any lab results from before your health system adopted the 2021 equation may not reflect your actual kidney status at that time. If you have concerns about your kidney health or notice that your eGFR has appeared to drop between older and newer lab results, the change in formula rather than an actual decline in function could be the explanation.
Most major U.S. health systems and laboratories have now switched to the race-neutral 2021 CKD-EPI equation. Your current lab results should already reflect the updated calculation. If your eGFR is in a borderline range, asking about a cystatin C test can provide a more precise picture of your kidney function.