eGFR Calculator (CKD-EPI 2021)
Estimate your Glomerular Filtration Rate using serum creatinine, age, and biological sex. This tool utilizes the CKD-EPI 2021 equation, which is recommended by the National Kidney Foundation.
Medical Disclaimer: This tool is for informational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a physician regarding kidney health.
Understanding the Glomerular Filtration Rate Formula
The Glomerular Filtration Rate (GFR) is widely considered the best overall index of kidney function. In health, the kidneys filter the blood to remove waste products like creatinine and urea. When the kidneys are damaged, their ability to filter decreases, causing waste products to build up in the blood.
Directly measuring GFR is difficult and requires injecting substances (like inulin) and monitoring their clearance over hours. Therefore, in clinical practice, doctors use an estimated GFR (eGFR) based on a formula using the blood level of creatinine, which is an endogenous muscle breakdown product.
The CKD-EPI 2021 Formula
The calculator above uses the CKD-EPI 2021 Creatinine Equation. This is the most modern standard recommended by the National Kidney Foundation and the American Society of Nephrology. It replaced older equations (like MDRD) and the 2009 CKD-EPI version to provide a more accurate estimate without using race as a variable.
The mathematical representation of the formula is:
Where:
- Scr is serum creatinine in mg/dL.
- κ (kappa) is 0.7 for females and 0.9 for males.
- α (alpha) is -0.241 for females and -0.302 for males.
- min indicates the minimum of Scr/κ or 1.
- max indicates the maximum of Scr/κ or 1.
Why Serum Creatinine Matters
Creatinine is a waste product generated by normal muscle wear and tear. Healthy kidneys filter creatinine out of the blood and into the urine. If your kidneys aren't working well, creatinine builds up in your blood. However, because creatinine production is linked to muscle mass, the formula adjusts for gender (as a proxy for muscle mass) and age to derive an accurate filtration rate.
Interpreting Your eGFR Results
The result is expressed in milliliters per minute per 1.73 square meters of body surface area (mL/min/1.73m²). This number generally corresponds to the percentage of available kidney function.
| eGFR Range | CKD Stage | Description |
|---|---|---|
| 90 + | Stage 1 | Normal kidney function (unless other signs of kidney damage like protein in urine are present). |
| 60 – 89 | Stage 2 | Mildly reduced kidney function. |
| 45 – 59 | Stage 3a | Mild to moderate loss of kidney function. |
| 30 – 44 | Stage 3b | Moderate to severe loss of kidney function. |
| 15 – 29 | Stage 4 | Severe loss of kidney function. Preparation for dialysis or transplant typically begins here. |
| Below 15 | Stage 5 | Kidney failure (End Stage Renal Disease). Dialysis or transplant is necessary for survival. |
Factors Affecting Accuracy
While the calculate glomerular filtration rate formula is a powerful diagnostic tool, certain factors can affect its accuracy:
- Muscle Mass: Bodybuilders may have high creatinine despite healthy kidneys, leading to a falsely low eGFR. Conversely, those with muscle wasting may have a falsely high eGFR.
- Diet: High protein intake or creatine supplements can temporarily raise creatinine levels.
- Acute Illness: The formula assumes stable kidney function. In cases of acute kidney injury (sudden failure), the eGFR may not accurately reflect current function.
Always review your results with a healthcare provider who can interpret them in the context of your overall health history.