Note: This is an estimate. Please consult a healthcare professional for clinical diagnosis.
What is Glomerular Filtration Rate (GFR)?
Glomerular Filtration Rate (GFR) is the primary metric used by medical professionals to determine how well the kidneys are functioning. It measures the rate at which blood passes through the glomeruli, which are the tiny filters in the kidneys that remove waste from the blood.
This calculator uses the CKD-EPI 2021 formula, which is currently the recommended standard by the National Kidney Foundation (NKF). Unlike older formulas, the 2021 version provides a more accurate estimate without requiring race as a variable, ensuring more equitable healthcare assessments.
Understanding Your Results
GFR results are typically categorized into stages of Chronic Kidney Disease (CKD):
| Stage | GFR Range | Interpretation |
|---|---|---|
| Stage 1 | 90 or higher | Normal kidney function (if protein is present) |
| Stage 2 | 60 – 89 | Mildly decreased 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 function |
| Stage 5 | Less than 15 | Kidney failure (ESRD) |
Calculation Example
If a 55-year-old male has a serum creatinine level of 1.2 mg/dL, his estimated GFR would be approximately 76 mL/min/1.73 m². This would place him in Stage 2, indicating mildly decreased kidney function, which often requires monitoring and lifestyle adjustments but may not indicate progressive disease in the absence of other symptoms like proteinuria.
Factors Influencing GFR
- Serum Creatinine: A waste product from muscle breakdown; higher levels usually indicate lower kidney function.
- Age: Kidney function naturally declines as we age, roughly by 1 mL/min per year after age 40.
- Biological Sex: Men generally have higher muscle mass, which leads to different baseline creatinine levels compared to women.
- Hydration: Severe dehydration can temporarily affect creatinine levels and GFR results.