GFR Calculator

GFR Calculator

Estimate your Glomerular Filtration Rate (GFR) using three prevalent formulas.

Estimated GFR Results

CKD-EPI Formula
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MDRD Formula
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Cockcroft-Gault Formula
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Disclaimer: This calculator provides estimates only. GFR values should be interpreted by a healthcare professional. Results are based on standard formulas and may not be accurate for all individuals.

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Understanding Your GFR: A Complete Guide to Glomerular Filtration Rate

Meta Description: What is a GFR test? Learn why Glomerular Filtration Rate is the key measure of kidney function, understand your GFR numbers by age and CKD stage, and discover how it’s calculated.

What is Glomerular Filtration Rate (GFR)?

Your Glomerular Filtration Rate (GFR) is the single best indicator of how well your kidneys are working. Think of it as a flow rate: it measures how much blood your kidneys’ tiny filters (glomeruli) can process per minute. A higher GFR typically signifies efficient kidney function, while a persistently low GFR can be a critical sign of kidney disease.

Monitoring your GFR is essential for the early detection and management of kidney-related health issues.

What Do Normal GFR Levels Look Like?

A “normal” GFR is influenced by several factors, including age, sex, and body size. For young, healthy adults, a normal GFR is often above 90 mL/min/1.73m². However, it’s natural for GFR to gradually decline with age.

Here is a general reference for average estimated GFR values by age group:

Age RangeAverage Estimated GFR (mL/min/1.73 m²)
20-29116
30-39107
40-4999
50-5993
60-6985
70+75

GFR and the Stages of Chronic Kidney Disease (CKD)

Doctors use GFR as a primary tool to diagnose and stage Chronic Kidney Disease (CKD). It’s important to note that a single GFR reading just below 60 may not immediately indicate CKD if you are older. Diagnosis often involves tracking GFR over time and checking for other markers like protein in the urine (proteinuria).

The five stages of CKD are defined by GFR ranges:

CKD StageDescriptionGFR Level (mL/min/1.73 m²)
Stage 1Kidney damage with normal function90+
Stage 2Kidney damage with mild loss of function60 – 89
Stage 3Moderate loss of kidney function30 – 59
Stage 4Severe loss of kidney function15 – 29
Stage 5Kidney Failure< 15

Early diagnosis at Stage 1 or 2 is crucial, as it allows for interventions that can significantly slow the disease’s progression and delay or prevent the need for dialysis.

How is GFR Measured and Estimated?

The most accurate way to measure GFR is through a complex process called inulin clearance. Because this test is invasive and impractical for everyday use, clinicians rely on estimation formulas (eGFR) that use a simple blood test for creatinine.

Creatinine is a waste product from muscle metabolism. Your kidneys filter it out of your blood. By measuring the creatinine level in your blood, along with key factors like age, sex, and race that influence its production, doctors can accurately estimate your true GFR.

Common eGFR formulas include:

  1. CKD-EPI Equation: Currently the most widely used and accurate formula for general clinical practice.
  2. MDRD Equation: A well-validated formula that is common in many lab reports.
  3. Schwartz Formula: The standard formula used for estimating GFR in children, which factors in the child’s height.

These formulas automatically account for variables to provide a personalized and accurate assessment of your kidney health.

Why Monitoring Your GFR is Vital

Your GFR is more than just a number—it’s a vital sign for your kidney health. Regular monitoring can:

  • Detect kidney disease early, often before symptoms appear.
  • Help your doctor determine the right dosage for medications processed by the kidneys.
  • Track the progression of known kidney disease and the effectiveness of treatment.

If you have risk factors like high blood pressure, diabetes, or a family history of kidney disease, discussing GFR testing with your doctor is a critical step for your long-term health.

Disclaimer: This information is for educational purposes only. Always consult with a healthcare professional for medical advice, diagnosis, and treatment.

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