Your lab report may show an Estimated Glomerular Filtration Rate (eGFR), a measure of your kidney health. This figure helps your healthcare provider understand how well your kidneys are performing their job of filtering waste from your blood. A higher eGFR number indicates better kidney function, while a lower number might suggest they are not working as efficiently. This estimate is derived from a simple blood test and is a standard part of routine health screenings.
Creatinine and Its Role in Measuring Kidney Function
The eGFR calculation begins with a measurement of creatinine in your blood. Creatinine is a waste product from the normal breakdown of muscle tissue, and its level is influenced by factors such as age, sex, and muscle mass. Because it is generated at a relatively steady rate, it serves as a useful marker for kidney function.
Healthy kidneys efficiently filter creatinine out of the blood and excrete it through urine. When kidney function declines, they are less effective at this filtration process, causing creatinine levels in the blood to rise. This relationship forms the basis of the eGFR test.
Directly measuring the glomerular filtration rate is a complex procedure, making it impractical for routine clinical use. Instead, healthcare professionals rely on the serum creatinine level, along with other variables, to calculate an estimated GFR. This estimation provides a practical way to monitor kidney health.
The Historical Race-Based eGFR Calculation
Until recently, standard eGFR calculations produced two different values: one for individuals identified as “African American” and another for “Non-African American.” This practice stemmed from older formulas, such as the Modification of Diet in Renal Disease (MDRD) and the original Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equations. Labs would often report both numbers because the patient’s race was not always known.
The rationale for this adjustment was rooted in population studies that found, on average, people who self-identified as Black had higher creatinine levels than people of other races, even at similar levels of kidney function. This statistical difference was attributed to a higher average muscle mass in the Black population group studied. The race variable was a statistical tool to adjust for these higher baseline creatinine levels, not a direct biological or genetic distinction.
The use of this adjustment, however, was problematic. Applying a population-level average to an individual can be inaccurate. The higher eGFR value generated by the race-based formula could mask the early stages of kidney disease in Black individuals, delaying diagnosis and contributing to existing health disparities.
The Transition to a Single, Race-Free Equation
In response to growing concerns, the medical community moved to eliminate race as a variable in eGFR calculations. This shift was driven by the recognition that race is a social construct, not a biological one, and is an unreliable proxy for muscle mass in any given individual. The use of a race-based adjustment was seen as perpetuating health inequities by systematically overestimating kidney function in Black patients.
In 2021, a task force from the National Kidney Foundation (NKF) and the American Society of Nephrology (ASN) recommended the adoption of a new, race-free formula. The 2021 CKD-EPI creatinine equation was developed to provide a more equitable estimation of GFR for everyone. This updated formula calculates a single eGFR value using serum creatinine, age, and sex, and helps ensure Black individuals receive more timely diagnoses. Most laboratories have now transitioned to this single, race-free calculation.
Understanding Your eGFR Number
Your eGFR result helps place your kidney function on a scale. An eGFR of 60 or higher is considered within the normal range. If your eGFR is below 60 for three months or more, it may indicate chronic kidney disease (CKD). An eGFR below 15 is a sign of kidney failure.
Healthcare providers use the eGFR to stage kidney disease, which helps guide treatment decisions. An eGFR between 60 and 89 might be classified as Stage 2 CKD if other signs of kidney damage, like protein in the urine, are present. Values between 30 and 59 indicate moderate kidney damage (Stage 3), while numbers between 15 and 29 suggest severe damage (Stage 4).
A single eGFR reading does not tell the whole story, and your healthcare provider will look at trends over time, as fluctuations can occur. Factors like being pregnant, very muscular, or very overweight can affect the accuracy of the estimate. Always discuss your results with your provider, who can interpret them in the context of your overall health.