GFR Calculation Formula
Estimate kidney function using the 2021 CKD-EPI Creatinine Equation
What is GFR and Why is it Important?
Glomerular Filtration Rate (GFR) is the best overall index of kidney function. It estimates how much blood passes through the glomeruli (tiny filters in the kidneys) each minute. Measuring GFR directly is complicated and expensive, so doctors use a calculation called eGFR (estimated GFR) based on a simple blood test for creatinine.
The CKD-EPI 2021 Calculation Formula
This calculator utilizes the 2021 CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) creatinine equation, which is currently the gold standard for clinical use. Unlike older versions, the 2021 update does not include a race-based coefficient, providing a more equitable assessment of kidney health.
The math behind the 2021 CKD-EPI formula is as follows:
- For Females: eGFR = 142 × min(Cr/0.7, 1)-0.241 × max(Cr/0.7, 1)-1.200 × 0.9938Age × 1.012
- For Males: eGFR = 142 × min(Cr/0.9, 1)-0.302 × max(Cr/0.9, 1)-1.200 × 0.9938Age
Stages of Chronic Kidney Disease (CKD)
Clinical professionals categorize kidney health into five stages based on the GFR value. Understanding these stages helps determine the necessary medical interventions.
| Stage | eGFR Range | Description |
|---|---|---|
| Stage 1 | 90 or above | Normal kidney function, but some evidence of kidney damage. |
| Stage 2 | 60 – 89 | Mildly decreased kidney function. |
| Stage 3a | 45 – 59 | Mildly to moderately decreased function. |
| Stage 3b | 30 – 44 | Moderately to severely decreased function. |
| Stage 4 | 15 – 29 | Severely decreased kidney function. |
| Stage 5 | Less than 15 | Kidney failure (ESRD). |
Calculation Example
If a 50-year-old male has a serum creatinine level of 1.2 mg/dL:
- We use the male formula constants (Cr = 1.2, Age = 50, K = 0.9, Alpha = -1.200).
- Inputting these values into the CKD-EPI 2021 formula results in an eGFR of approximately 76 mL/min/1.73 m².
- This would place the individual in Stage 2 (Mildly decreased function).
Disclaimer: This calculator is for educational purposes only. Always consult a qualified healthcare provider for medical diagnosis and treatment decisions.