What is the significance of the Black race coefficient in the estimated glomerular filtration rate (eGFR) calculation?

Significance of the Black Race Coefficient in eGFR Calculation

The Black race coefficient in eGFR equations should no longer be used—the 2021 CKD-EPI creatinine equation without any race variable is now the standard of care for all adults in the United States. 1, 2

Historical Context and the Problem

The race coefficient was originally included in eGFR equations because Black individuals in the development cohorts had approximately 16% higher measured GFR compared to non-Black individuals with identical age, sex, and serum creatinine levels. 3 This adjustment was intended to account for presumed differences in muscle mass and creatinine generation. 3

However, this race-based adjustment systematically overestimated kidney function in Black patients, creating profound clinical harms: 1, 2

• Delayed CKD diagnosis: Approximately 2 million Black adults in the U.S. would be reclassified as having CKD if race were removed from calculations 2
• Delayed nephrology referral: 260,000 fewer Black adults met referral thresholds when race was included 2
• Reduced transplant access: 290,000 additional Black adults (a 29% increase) would meet transplant referral thresholds without the race coefficient 2
• Restricted access to kidney-protective medications: Fewer Black patients qualified for ACE inhibitors, ARBs, and SGLT2 inhibitors due to artificially elevated eGFR values 2

The 2022 NKF-ASN Task Force Solution

The National Kidney Foundation and American Society of Nephrology Task Force issued a strong recommendation in 2022 to immediately implement the 2021 CKD-EPI creatinine equation without race for all U.S. adults. 1, 2, 4

Key Performance Characteristics

The race-free 2021 CKD-EPI equation: 1, 2

• Reduces differential bias between Black and non-Black individuals from the prior race-based approach
• Maintains acceptable accuracy across diverse populations in external validation studies
• Requires no new laboratory infrastructure—it uses the same creatinine assay already in place

Statistical Impact of Removing Race

When race was removed from the equation: 1

• For Black adults: Bias changed from +3.7 to -3.8 mL/min/1.73 m² (underestimation of 3.8 vs. prior overestimation of 3.7)
• For non-Black adults: Bias changed from +0.5 to +2.4 mL/min/1.73 m² (overestimation increased from 0.5 to 2.4)

This trade-off was deemed acceptable because it eliminates systematic disadvantages for Black individuals while maintaining overall accuracy. 1, 2

Confirmatory Testing Strategy

For patients at risk for or with established CKD, add cystatin C measurement and use the 2021 CKD-EPI creatinine-cystatin C equation (also race-free). 2

This combined approach: 1, 2

• Provides greater accuracy than either creatinine or cystatin C alone
• Completely eliminates the need for race-based adjustments
• Reduces bias to 3.8 mL/min/1.73 m² in Black adults and 2.4 mL/min/1.73 m² in non-Black adults 1

What NOT to Do

There is no evidentiary basis for reporting two eGFR values (one with race, one without) or labeling them as "high/low muscle mass." 1 This approach:

• Introduces subjectivity and confusion 1
• May lead clinicians to incorrectly assume the true GFR falls between the two values 1
• Perpetuates the bias that race-based adjustments were designed to address 1

Clinical Decision-Making Guidance

When using the race-free equation: 2

• Do not base major decisions on a single eGFR result—confirm with repeat testing
• Monitor eGFR trends over time with more frequent testing when needed
• Incorporate albuminuria assessment as recommended by KDIGO guidelines
• For critical decisions (transplant eligibility, chemotherapy dosing, nephrotoxic drugs), use confirmatory cystatin C testing or direct GFR measurement

Medication Dosing Considerations

Use non-indexed eGFR values (mL/min) rather than indexed values (mL/min/1.73 m²) for medication dosing decisions. 2 This is particularly important in:

• Obese patients: Indexed eGFR systematically underestimates true GFR, risking medication underdosing 2
• Black women: Obesity prevalence is highest in this population, making de-indexing especially critical 2

Supporting Evidence from International Studies

A systematic review of 12 international studies found that removal of race adjustment improved bias, accuracy, and precision of eGFR equations for Black adults globally. 5 Studies from the United Kingdom demonstrated that ethnicity adjustment led to overestimation of measured GFR by approximately 20 mL/min/1.73 m² in Black participants, potentially reducing CKD diagnosis and under-recognition of disease severity. 6

Implementation Status

KDIGO Practice Point 1.2.4.2 explicitly states that race should be avoided in eGFR calculations. 2 The KDOQI Work Group endorses the race-free 2021 CKD-EPI equations for all adult patients. 2

Common Pitfalls to Avoid

• Do not continue using race-based equations—they create systematic disadvantages for Black patients 1, 2
• Do not report dual eGFR values—this adds confusion without improving accuracy 1
• Do not ignore body habitus when interpreting indexed eGFR in obese patients—consider de-indexing for medication dosing 2
• Do not rely solely on creatinine-based eGFR for critical decisions—use confirmatory cystatin C testing 2