Estimate Your GFR (CKD-EPI 2021)
Understanding the Glomerular Filtration Rate Formula
The Glomerular Filtration Rate (GFR) is widely considered the best overall index of kidney function in health and disease. It measures the volume of fluid filtered from the kidney's glomerular capillaries into the Bowman's capsule per unit of time. Because measuring GFR directly requires invasive procedures, medical professionals typically use the Estimated Glomerular Filtration Rate (eGFR) based on a blood test for serum creatinine.
How is eGFR Calculated?
This calculator utilizes the CKD-EPI (2021) Creatinine Equation, which is currently recommended by the National Kidney Foundation and the American Society of Nephrology. This specific formula was developed to provide a more accurate estimate of kidney function without relying on race as a variable, which was common in older equations like the MDRD or the 2009 CKD-EPI equation.
The variables required for the calculation are:
- Serum Creatinine: A waste product from the normal breakdown of muscle tissue. Healthy kidneys filter creatinine out of the blood.
- Age: GFR naturally declines with age.
- Gender: Men and women have different muscle mass averages, affecting creatinine generation.
Interpreting Your GFR Results
The results of an eGFR test are typically categorized into stages of Chronic Kidney Disease (CKD). A higher number generally indicates better kidney function.
- > 90 mL/min/1.73m²: Normal or high kidney function. If there is no protein in the urine or other signs of damage, this is healthy.
- 60 – 89 mL/min/1.73m²: Mildly decreased kidney function. This may be normal for older adults but warrants monitoring.
- 45 – 59 mL/min/1.73m² (Stage 3a): Mild to moderate decrease in kidney function.
- 30 – 44 mL/min/1.73m² (Stage 3b): Moderate to severe decrease in kidney function.
- 15 – 29 mL/min/1.73m² (Stage 4): Severe decrease in kidney function. Preparation for kidney replacement therapy usually begins here.
- < 15 mL/min/1.73m² (Stage 5): Kidney failure. Dialysis or a transplant is necessary to survive.
Why Use the CKD-EPI 2021 Formula?
Prior formulas often included a coefficient for "African American" or "Black" race, assuming higher muscle mass and creatinine generation. However, recent medical consensus has shifted to remove race from the calculation to ensure equitable healthcare and avoid delayed diagnosis for certain populations. The 2021 refit of the CKD-EPI equation provides a standardized approach applicable to all adults.
Disclaimer: This tool provides an estimate for informational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always consult with a healthcare provider regarding your kidney health.