The measurement of kidney function is expressed as the glomerular filtration rate (GFR), the total volume of fluid passing through the kidney’s filter every minute. Since that is difficult to determine in real-time, several factors are used to calculate an estimated rate (eGFR): serum creatinine, age, sex, and race. 

Using race as a factor in this equation has affected and will continue to affect decisions made in regards to care for people of color (POC), as research has shown. Two major kidney disease organizations, the American Society of Nephrology (ASN) and the National Kidney Foundation (NKF), came together to “reevaluate the long-standing use of including race in a calculation to diagnose kidney disease.”*

When did the criteria change?

Prior to the 1990s, eGFR had been calculated using body weight as a major factor, but researchers began claiming that body weight was affected by too many variables to be reliable. A landmark study in 1999 indicated that, when compared to White people, Black people had:

• Greater muscle mass
• Lower body fat
• Different body densities
• Higher total body potassium and calcium 
• Higher than average serum creatinine kinase levels

Higher values indicate better kidney function, which, in theory, would be a good sign. As a result of this study, race was included as a refinement of the eGFR calculation. This calculation has remained unchallenged until recently.

Why should this 1999 calculation be challenged?

Unfortunately, the 1999 inclusion of race in the eGFR equation was based on three small, flawed studies that involved just over 1,000 participants and considered very few factors. According to Nwamaka D. Eneanya, MD, MPH, a nephrologist and assistant professor of medicine at the Hospital of the University of Pennsylvania, these flawed findings should have been challenged long ago. 

Eneanya is part of the task force that was created in August 2020 by the ASN and NKF to reassess the value of including race in the calculation of eGFR. Speaking at this year’s ASN Kidney Week event, Eneanya discussed why the 1999 study results are unreliable and how racial inclusion in eGFR can result in health inequity.

Concerning the study results, she explained:

• Muscle mass can only be accurately measured on a cadaver, not in living people.
• Human genome studies confirm zero biological differences between races.
• More likely factors than race in the studies’ results include sociodemographic differences in clinical trial participation; diet (especially those that include meat); and medications.

In what ways is the inclusion of race in eGFR problematic?

Factoring in race based on inaccurate data results in higher eGFR numbers (i.e., an indication of better kidney function) for Black people. As a result, Black people with chronic kidney disease (CKD) are more likely to experience:

• Underdiagnosis
• Delayed referrals to specialty care
• Undertreatment
• Delayed and/or inaccurate dialysis or kidney transplant evaluation
• Insufficient medication dosing

A recent study showed that removing the factor of race resulted in one-third of Black patients being reclassified to a later, more progressed, stage of CKD. This reclassification led to increased attention being given to:

• Disease management  
• Dialysis planning
• Referrals for kidney transplants and specialty care

Drawbacks of removing race from the equation include the possibility that Black people will experience an overdiagnosis of CKD and, thus, potentially unnecessary treatments. 

In addition, Eneanya noted, the current eGFR calculation does not include guidelines for use with people of mixed race, a demographic that has been steadily increasing since 2000.

Is there a better solution?

Fortunately, there are more useful options; more institutions, including Beth Israel Deaconess Medical Center, Mass General Brigham, and the University of Washington, are moving away from relying strictly on eGFR.

Eneanya suggested looking to other data, such as:

• Cystatin C (cystatin 3), a protein in the blood, of which high levels may indicate poor kidney function 
• Tubular handling
• Extrarenal (non-kidney) elimination

Re-evaluating the foundations of long-accepted practices and treatment recommendation represents a critical step forward toward health equity and better outcomes. “False biological beliefs,” said Eneanya, “will absolutely affect clinical care.”

*Inserro, A. (2020, Oct. 25). Flawed Racial Assumptions in eGFR Have Care Implications in CKD. American Journal of Managed Care. https://www.ajmc.com/view/flawed-racial-assumptions-in-egfr-have-care-implications