Kidney Function Calculator (eGFR)
Calculate your estimated glomerular filtration rate (eGFR) to assess kidney function using the CKD-EPI equation, the most accurate formula recommended by medical professionals.
Your Kidney Function Results
Comprehensive Guide: How to Calculate Kidney Function
Understanding your kidney function is crucial for maintaining overall health, especially if you have risk factors like diabetes, high blood pressure, or a family history of kidney disease. The most common method to assess kidney function is by calculating the estimated glomerular filtration rate (eGFR), which measures how well your kidneys filter blood.
What is eGFR and Why is it Important?
The glomerular filtration rate (GFR) is the best overall measure of kidney function. It estimates how much blood passes through the glomeruli (tiny filters in the kidneys) each minute. A normal GFR varies by age, sex, and body size, but in young adults it’s typically 90-120 mL/min/1.73m².
Since measuring GFR directly is complex, doctors use formulas to estimate GFR (eGFR) based on:
- Serum creatinine level (a waste product from muscle metabolism)
- Age
- Sex
- Race (in some formulas)
- Body size (sometimes)
The CKD-EPI Equation: Most Accurate eGFR Formula
The Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation is currently the most accurate formula for estimating GFR in adults. It was developed in 2009 and is recommended by the National Kidney Foundation and National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK).
The CKD-EPI formula is more accurate than the older MDRD formula, especially for people with normal or near-normal kidney function (eGFR >60 mL/min/1.73m²).
How the CKD-EPI Formula Works
The CKD-EPI equation uses different formulas based on:
- Sex (male or female)
- Race (Black or non-Black in the original equation)
- Serum creatinine level
For creatinine ≤ 0.7 mg/dL (female) or ≤ 0.9 mg/dL (male):
eGFR = 142 × (min(Scr/κ, 1))α × (max(Scr/κ, 1))-1.200 × 0.993Age × 1.012 [if female] × 1.159 [if Black]
For creatinine > 0.7 mg/dL (female) or > 0.9 mg/dL (male):
eGFR = 142 × (min(Scr/κ, 1))α × (max(Scr/κ, 1))-0.349 × 0.993Age × 1.012 [if female] × 1.159 [if Black]
Where:
- Scr = serum creatinine in mg/dL
- κ = 0.7 (females) or 0.9 (males)
- α = -0.241 (females) or -0.302 (males)
- min = minimum of Scr/κ or 1
- max = maximum of Scr/κ or 1
Understanding Your eGFR Results
Your eGFR number helps determine your stage of kidney disease:
| Stage | eGFR (mL/min/1.73m²) | Description | Actions Recommended |
|---|---|---|---|
| 1 | >90 | Normal kidney function | Maintain healthy lifestyle |
| 2 | 60-89 | Mildly reduced function | Monitor, control risk factors |
| 3a | 45-59 | Mild to moderate reduction | Evaluate for cause, treat complications |
| 3b | 30-44 | Moderate to severe reduction | Prepare for possible kidney failure |
| 4 | 15-29 | Severe reduction | Plan for kidney replacement therapy |
| 5 | <15 | Kidney failure | Start kidney replacement therapy |
Factors That Affect eGFR Accuracy
While eGFR is the best estimate of kidney function available without invasive tests, several factors can affect its accuracy:
For these individuals, additional tests like cystatin C (another blood marker) or 24-hour urine collection for creatinine clearance may provide more accurate results.
Alternative Methods to Assess Kidney Function
While eGFR is the standard, other tests can provide additional information:
| Test | What It Measures | When It’s Used | Normal Range |
|---|---|---|---|
| Serum Creatinine | Waste product from muscle metabolism | Standard kidney function test | 0.6-1.2 mg/dL (varies by sex/muscle mass) |
| BUN (Blood Urea Nitrogen) | Another waste product filtered by kidneys | General kidney function screening | 7-20 mg/dL |
| Cystatin C | Protein produced by cells, filtered by kidneys | When creatinine may be misleading | 0.5-1.0 mg/L |
| Urinalysis | Protein, blood, or other abnormalities in urine | Screening for kidney damage | Negative for protein/blood |
| 24-hour Urine Collection | Creates clearance measurement | When eGFR may be inaccurate | 80-120 mL/min |
How to Improve or Maintain Kidney Function
If your eGFR shows reduced kidney function, these steps can help protect your kidneys:
- Control blood pressure – Aim for <130/80 mmHg (or <120/80 if you have diabetes or protein in urine)
- Manage blood sugar – Keep HbA1c <7% if you have diabetes
- Stay hydrated – Drink enough water but avoid excessive fluid intake
- Eat a kidney-friendly diet – Limit sodium, phosphorus, and potassium if needed
- Avoid NSAIDs – Ibuprofen, naproxen can harm kidneys with long-term use
- Exercise regularly – Aim for 150 minutes of moderate activity per week
- Don’t smoke – Smoking damages blood vessels and reduces kidney function
- Limit alcohol – No more than 1 drink per day for women, 2 for men
- Maintain healthy weight – BMI between 18.5-24.9
- Get regular check-ups – Especially if you have risk factors
When to See a Doctor About Kidney Function
Consult a healthcare provider if you:
- Have an eGFR <60 for 3+ months (possible chronic kidney disease)
- Notice sudden drops in eGFR (possible acute kidney injury)
- Have symptoms like swelling, fatigue, or frequent urination
- Have risk factors (diabetes, high blood pressure, family history)
- Are over age 60 (kidney function naturally declines with age)
A nephrologist (kidney specialist) can perform more detailed evaluations if needed, including:
- Kidney biopsy
- Advanced imaging (CT scan, MRI, or ultrasound)
- Specialized blood tests
- Genetic testing for inherited kidney diseases
Common Questions About Kidney Function
Can eGFR fluctuate?
Yes, eGFR can vary slightly due to:
- Hydration status (dehydration can temporarily lower eGFR)
- Recent meat consumption (can temporarily raise creatinine)
- Illness or infection
- Certain medications
For diagnosis, doctors look at eGFR over time, not just one measurement.
Is there a “normal” eGFR for my age?
eGFR naturally declines with age. While 90-120 is considered normal for young adults, these are general guidelines by age:
- 20-29 years: 90-115 mL/min/1.73m²
- 30-39 years: 85-110 mL/min/1.73m²
- 40-49 years: 80-105 mL/min/1.73m²
- 50-59 years: 75-100 mL/min/1.73m²
- 60-69 years: 70-95 mL/min/1.73m²
- 70+ years: 60-85 mL/min/1.73m²
Can I have normal creatinine but low eGFR?
Yes, this can happen because eGFR considers age, sex, and race in addition to creatinine. For example:
- An older person with “normal” creatinine might have low eGFR due to age-related muscle loss
- A small-framed woman might have low eGFR with normal creatinine
What’s the difference between GFR and eGFR?
GFR (Glomerular Filtration Rate) is the actual measurement of kidney function, while eGFR is an estimate calculated from a formula. True GFR measurement requires:
- Intravenous infusion of a marker substance (like inulin)
- Multiple blood and urine samples over several hours
- Specialized laboratory analysis
This is why eGFR is used in clinical practice – it’s much more convenient while still being accurate for most people.