GFR (eGFR) Calculator
Estimate kidney function using the CKD-EPI, MDRD, and Cockcroft-Gault formulas.
Medical Disclaimer: This tool provides estimates for informational purposes only and is not a substitute for professional medical assessment. For diagnosis or treatment, consult a healthcare professional.
What is eGFR and Why It Matters
eGFR stands for estimated Glomerular Filtration Rate. It's a key indicator of kidney function. Your kidneys have tiny filters called glomeruli that help remove waste and excess fluid from the blood. The GFR is a measurement of how much blood these filters clean each minute.
Since measuring the GFR directly is a complex process, doctors use a mathematical formula to estimate it based on a few factors from your blood test and personal data. This estimate is the eGFR. A lower eGFR number may indicate that your kidneys are not working as well as they should. Tracking eGFR over time can help doctors detect kidney disease early and monitor its progression.
How eGFR Is Calculated (CKD-EPI, MDRD, Cockcroft-Gault)
Several different formulas have been developed to estimate GFR. This calculator provides results from the most common ones:
- CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration): This is the most current and widely recommended formula for adults. The original 2009 version used a race coefficient. However, the latest 2021 CKD-EPI equation has removed this variable to provide a more equitable and equally accurate estimation. This calculator defaults to the 2021 race-free equation unless a race is specified for comparison with older formulas.
- MDRD (Modification of Diet in Renal Disease Study): This was the most common formula used before CKD-EPI. It is known to be less accurate than CKD-EPI, especially at higher GFR values (e.g., above 60 mL/min/1.73 m²).
- Cockcroft-Gault: This formula is one of the oldest and is used to estimate creatinine clearance (CrCl), not GFR directly. While CrCl is similar to GFR, they are not the same. This formula heavily relies on weight and is still frequently used to adjust medication dosages for patients with kidney disease.
BSA Normalization
eGFR is typically "normalized" to a standard body surface area (BSA) of 1.73 m². This allows for a fair comparison of kidney function between people of different sizes. This calculator computes your BSA using the DuBois & DuBois formula if you provide your height and weight.
When to Use eGFR vs. Creatinine Clearance
eGFR is the preferred test for assessing and staging chronic kidney disease (CKD). It provides a standardized measure of overall kidney filtration function.
Creatinine Clearance (CrCl), estimated by the Cockcroft-Gault formula, is primarily used for drug dosing. Many pharmaceutical companies base their dosage adjustment recommendations on CrCl values, which is why it remains clinically relevant despite being an older method.
Limitations & When to See a Doctor
eGFR calculations are only estimates and have limitations. The formulas are less accurate in certain populations, including:
- Individuals with rapidly changing kidney function (acute kidney injury).
- People with extreme body sizes or muscle mass (e.g., bodybuilders, amputees).
- Those on unusual diets (e.g., high-protein, creatine supplements).
- During pregnancy, as kidney function changes significantly.
- Very young or very old individuals.
You should always consult a healthcare professional to interpret your eGFR results. A single low reading may not be a cause for alarm, but a persistently low or declining eGFR requires medical evaluation to determine the cause and appropriate management.
Frequently Asked Questions
Q: What is a normal eGFR?
A: For most healthy adults, a normal eGFR is 90 or above. However, eGFR naturally declines with age. An eGFR below 60 mL/min/1.73 m² for three months or more is a sign of chronic kidney disease.
Q: Can I improve my eGFR?
A: While you can't reverse damage that has already occurred, you can take steps to protect your existing kidney function. This includes managing blood pressure, controlling blood sugar (if you have diabetes), eating a healthy diet, avoiding certain medications (like NSAIDs), and not smoking.
Q: What are the stages of Chronic Kidney Disease (CKD)?
A: CKD is staged based on eGFR levels: Stage G1: ≥90 (Normal or high); Stage G2: 60-89 (Mildly decreased); Stage G3a: 45-59 (Mild to moderate); Stage G3b: 30-44 (Moderate to severe); Stage G4: 15-29 (Severely decreased); Stage G5: <15 (Kidney failure).
Q: Why was race removed from the new CKD-EPI formula?
A: The race coefficient was removed because race is a social construct, not a biological one. Research showed that removing it led to a more equitable and equally accurate estimation of kidney function across different populations, reducing disparities in diagnosis and treatment.
Q: What is Cystatin C?
A: Cystatin C is another protein produced by the body and filtered by the kidneys. Sometimes, a blood test for Cystatin C is used along with creatinine to get a more accurate eGFR, especially when the creatinine-based result is borderline or unexpected.
Q: Does my diet affect my creatinine level?
A: Yes. Creatinine is a byproduct of muscle metabolism and is also found in cooked meat. Eating large amounts of meat before a blood test can slightly increase your creatinine level and temporarily lower your eGFR.
