GFR Calculator (CKD-EPI 2021)

What is Glomerular Filtration Rate (GFR)?

The Glomerular Filtration Rate (GFR) is the best overall index of kidney function. Your kidneys contain millions of tiny filtering units called glomeruli. The GFR test estimates how much blood passes through these filters each minute. A low GFR indicates that your kidneys are not working as well as they should and may be a sign of chronic kidney disease (CKD). This eGFR calculator uses the CKD-EPI 2021 Creatinine Equation, the most up-to-date formula recommended by the National Kidney Foundation, to provide an estimated GFR (eGFR) based on your serum creatinine level, age, and sex.

The Stages of Chronic Kidney Disease (CKD)

Your eGFR result corresponds to a specific stage of CKD, which helps doctors understand the severity of kidney damage and plan treatment accordingly:

• Stage 1 (GFR ≥ 90): Normal or high kidney function, but with other signs of kidney damage (like protein in the urine).
• Stage 2 (GFR 60-89): Mildly decreased kidney function with other signs of kidney damage.
• Stage 3a (GFR 45-59): Mildly to moderately decreased kidney function.
• Stage 3b (GFR 30-44): Moderately to severely decreased kidney function.
• Stage 4 (GFR 15-29): Severely decreased kidney function.
• Stage 5 (GFR < 15): Kidney failure, often requiring dialysis or a transplant.

Why the CKD-EPI 2021 Equation?

For many years, GFR estimation equations included a coefficient for race (Black/non-Black). However, extensive research demonstrated that this practice was not scientifically justified and contributed to health disparities. In 2021, the National Kidney Foundation and the American Society of Nephrology task force recommended the adoption of the new CKD-EPI Creatinine Equation (2021), which removes the race variable. This calculator uses this new, more equitable formula to provide a more accurate estimation for all individuals.

Limitations and Next Steps

While an eGFR calculation is a crucial screening tool, it has limitations. The formula is less accurate in people who are very muscular (like bodybuilders), those with a very low muscle mass, or during acute illness. A single eGFR result doesn't diagnose kidney disease; doctors look at the trend over time. Your overall health profile, including your BMI and blood pressure, also plays a significant role in kidney health. For more information, the National Kidney Foundation provides excellent patient resources.