GFR Calculator

Estimate Glomerular Filtration Rate for Kidney Function Assessment

Gender

Age years

Ethnicity

Serum Creatinine mg/dL

Kidney Function Assessment

-- mL/min/1.73m²

Normal Stage 1-2 Stage 3 Stage 4 Stage 5

Interpretation

Recommendations

What is GFR?

Glomerular Filtration Rate (GFR) is the best test to measure your level of kidney function and determine your stage of kidney disease. Your GFR number tells you how much kidney function you have and is considered the most accurate measure of kidney function.

GFR is calculated from the results of a blood test that measures your creatinine levels along with your age, gender, and ethnicity. The normal GFR rate is 90 or above. GFR below 60 for three months or more may indicate chronic kidney disease.

How GFR is Calculated

The CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) formula is the current standard for estimating GFR:


                    CKD-EPI Formula Components:

                    • Serum creatinine level

                    • Age

                    • Gender

                    • Ethnicity (Black or Non-Black)


                    
                    Calculation Method:

                    GFR = 141 × min(SCr/κ, 1)^α × max(SCr/κ, 1)^-1.209 × 0.993^Age × 1.018 [if female] × 1.159 [if Black]


                    
                    Where:

                    • SCr = serum creatinine

                    • κ = 0.7 (females) or 0.9 (males)

                    • α = -0.329 (females) or -0.411 (males)

This advanced formula provides more accurate GFR estimates, especially at higher levels of kidney function, compared to older calculation methods.

Chronic Kidney Disease (CKD) Stages

Stage 1: Kidney damage with normal GFR (90 or higher)

Kidney function is normal but there is evidence of kidney damage (protein in urine, abnormalities in imaging). Early detection and treatment can prevent progression.

Stage 2: Mildly reduced GFR (60-89)

Mild loss of kidney function with evidence of kidney damage. Monitoring and lifestyle modifications are important to slow progression.

Stage 3: Moderately reduced GFR (30-59)

Moderate loss of kidney function. Often divided into 3A (45-59) and 3B (30-44). Complications like anemia and bone disease may begin.

Stage 4: Severely reduced GFR (15-29)

Severe loss of kidney function. Preparation for kidney replacement therapy should begin. Symptoms become more noticeable.

Stage 5: Kidney failure (GFR less than 15)

End-stage renal disease requiring dialysis or kidney transplantation. Waste products build up to dangerous levels.

Improving Kidney Health

You can protect your kidney function through evidence-based strategies:

Blood Pressure Control: Maintain BP below 130/80 mmHg
Blood Sugar Management: Keep HbA1c below 7% if diabetic
Healthy Diet: Reduce sodium, limit protein if needed, increase fruits/vegetables
Hydration: Drink adequate water unless fluid-restricted
Medication Review: Avoid NSAIDs and other kidney-damaging drugs
Smoking Cessation: Eliminate tobacco completely
Regular Exercise: 30 minutes most days of the week
Weight Management: Maintain healthy BMI
Limit Alcohol: Moderate consumption as recommended

Early detection and proper management can significantly slow the progression of kidney disease and prevent complications.

GFR Calculator FAQs

How accurate is the GFR calculation?

The CKD-EPI formula provides a highly accurate estimate of true kidney function for most people. However, it may be less accurate in certain populations like pregnant women, severely malnourished individuals, or those with unusual muscle mass. For precise assessment, measured GFR tests are available but are more complex and expensive.

Why is ethnicity a factor in GFR calculation?

Research shows that Black individuals tend to have higher muscle mass and creatinine production, which affects GFR calculations. The ethnicity adjustment provides a more accurate estimation of true kidney function across different populations. This is based on large population studies and helps prevent misclassification of kidney disease.

When should I see a doctor about my GFR results?

You should consult a healthcare provider if your GFR is consistently below 60 mL/min/1.73m², if there's a rapid decline in GFR (drop of more than 5 mL/min/1.73m² per year), or if you have other risk factors for kidney disease such as diabetes, hypertension, or family history of kidney disease.

Can GFR improve or is kidney damage permanent?

While established kidney scarring is permanent, GFR can stabilize or even improve slightly with proper treatment of underlying conditions. Controlling blood pressure, managing diabetes, and avoiding kidney-toxic substances can prevent further decline and in some cases lead to modest improvement in kidney function.

What other tests are important for kidney health?

Comprehensive kidney assessment should include urine albumin-to-creatinine ratio (measures protein leakage), blood pressure monitoring, and basic metabolic panel. Imaging tests like kidney ultrasound may be needed if structural abnormalities are suspected. Regular monitoring helps detect kidney disease in its earliest stages.