GFR Calculator
GFR Calculator
Estimate Glomerular Filtration Rate (eGFR) using the CKD-EPI 2021 formula.
A Window into Kidney Health: The GFR Calculator
Disclaimer: This calculator is intended for informational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition.
The Glomerular Filtration Rate (GFR) is the single most important test used to measure the level of kidney function and determine the stage of kidney disease. Your kidneys are vital organs that filter waste products and excess fluid from your blood to produce urine. The glomeruli are tiny filters within your kidneys. The GFR is a calculation of how much blood passes through these filters each minute. A normal GFR indicates that your kidneys are working well. A GFR below normal levels suggests that your kidneys are not filtering blood as efficiently as they should be, which can be an early sign of chronic kidney disease (CKD).
Directly measuring GFR is a complex procedure. Therefore, healthcare providers use a formula to calculate an *estimated* GFR, or eGFR. This calculator uses the 2021 CKD-EPI Creatinine Equation, which is the most current and recommended formula for estimating GFR in adults. It is based on your serum creatinine level, age, and sex. By providing these values, this tool can give you an eGFR score that helps you and your doctor understand your kidney function and track it over time.
The CKD-EPI 2021 Formula
The Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation is a complex formula that provides a more accurate estimate of GFR than previous formulas, especially at higher GFR levels. The 2021 revision of this formula removed race as a variable, promoting health equity in the diagnosis of kidney disease.
The formula is: eGFR = 142 × min(S_cr / κ, 1)ᵃ × max(S_cr / κ, 1)⁻¹.²⁰⁰ × 0.9938^Age × (1.012 if Female)
- S_cr is the serum creatinine in mg/dL.
- κ (kappa) is a constant: 0.7 for females and 0.9 for males.
- α (alpha) is a constant: -0.241 for females and -0.302 for males.
- Age is the patient's age in years.
This calculator handles this complex formula for you, providing a simple and accessible result.
Understanding Your eGFR Result: Stages of Chronic Kidney Disease (CKD)
The National Kidney Foundation uses eGFR to classify the stages of CKD:
| Stage | eGFR Level (mL/min/1.73m²) | Description |
|---|---|---|
| Stage 1 | 90 or higher | Normal kidney function, but with signs of kidney damage (e.g., protein in urine). |
| Stage 2 | 60-89 | Mildly reduced kidney function, with other signs of kidney damage. |
| Stage 3a | 45-59 | Mild to moderately reduced kidney function. |
| Stage 3b | 30-44 | Moderately to severely reduced kidney function. |
| Stage 4 | 15-29 | Severely reduced kidney function. |
| Stage 5 | Less than 15 | Kidney failure (end-stage renal disease), often requiring dialysis or transplant. |