eGFR Calculator using Creatinine and Urea
Enter the value from your blood test.
Enter your BUN value. This is used for the BUN:Creatinine ratio.
Enter your age in years.
Select the sex assigned at birth, as it affects the calculation.
Your Estimated GFR (eGFR)
mL/min/1.73m²
CKD Stage
—
BUN:Creatinine Ratio
—
Formula Parameters
κ: –, α: —
Formula Used: This calculator uses the 2021 CKD-EPI Creatinine Equation, which is the current standard for estimating GFR. It no longer uses a race coefficient. The formula is: eGFR = 142 × min(SCr/κ, 1)α × max(SCr/κ, 1)-1.200 × 0.9938Age × (1.012 if Female).
Understanding Your Results
| Stage | eGFR Level (mL/min/1.73m²) | Description |
|---|---|---|
| G1 | ≥ 90 | Normal or high kidney function |
| G2 | 60-89 | Mildly decreased kidney function |
| G3a | 45-59 | Mildly to moderately decreased kidney function |
| G3b | 30-44 | Moderately to severely decreased kidney function |
| G4 | 15-29 | Severely decreased kidney function |
| G5 | < 15 | Kidney failure |
What is an eGFR Calculator using Creatinine and Urea?
An estimated Glomerular Filtration Rate (eGFR) is a crucial measure of kidney function. The eGFR calculator using creatinine and urea is a digital tool that provides this vital health metric. It primarily uses a blood test result for creatinine, along with your age and sex, to calculate how well your kidneys are filtering waste from your blood. While urea (measured as Blood Urea Nitrogen or BUN) is not a direct input into the standard eGFR formula, it’s a critical secondary marker. This calculator also computes the BUN-to-creatinine ratio, which gives doctors additional clues about the cause of kidney issues.
This calculator is for anyone wanting to monitor their kidney health, especially individuals with risk factors for chronic kidney disease (CKD) such as diabetes, high blood pressure, or a family history of kidney problems. A common misconception is that eGFR is a direct measurement. In reality, it is a highly accurate *estimate* based on population data, providing a practical and reliable way to track kidney function over time.
eGFR Formula and Mathematical Explanation
This calculator employs the 2021 Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) creatinine equation. This is the most current, race-free formula recommended by the National Kidney Foundation.
The core formula is:
eGFR = 142 × min(SCr/κ, 1)α × max(SCr/κ, 1)-1.200 × 0.9938Age × (1.012 if Female)
The calculation involves several steps:
- Normalize Creatinine: The patient’s serum creatinine (SCr) is divided by a constant, kappa (κ), which varies by sex.
- Apply Exponents: The formula uses `min` and `max` functions to apply different exponents based on whether the normalized creatinine is below or above 1. This two-slope approach improves accuracy across different ranges of kidney function.
- Adjust for Age: The result is multiplied by 0.9938 raised to the power of the patient’s age.
- Adjust for Sex: For females, the result is multiplied by a factor of 1.012.
In addition, the BUN-to-Creatinine ratio is calculated, which is a simple division of the BUN value by the creatinine value (both in mg/dL). A typical range is 10:1 to 20:1. Ratios outside this range can suggest issues like dehydration or other conditions affecting kidney function.
| Variable | Meaning | Unit | Typical Range |
|---|---|---|---|
| SCr | Serum Creatinine | mg/dL | 0.6–1.3 |
| BUN | Blood Urea Nitrogen | mg/dL | 7–20 |
| Age | Patient’s Age | Years | 18+ |
| κ (Kappa) | Sex-specific constant | N/A | 0.7 (Female), 0.9 (Male) |
| α (Alpha) | Sex-specific exponent | N/A | -0.241 (Female), -0.302 (Male) |
Practical Examples
Example 1: Middle-Aged Male with Mildly Elevated Creatinine
- Inputs: Serum Creatinine: 1.4 mg/dL, BUN: 25 mg/dL, Age: 60, Sex: Male
- eGFR Calculation: The calculator processes these inputs through the CKD-EPI formula, resulting in an eGFR of approximately 58 mL/min/1.73m².
- BUN:Creatinine Ratio: 25 / 1.4 ≈ 17.9:1.
- Interpretation: The eGFR of 58 places him in Stage G3a, indicating mildly to moderately decreased kidney function. The BUN:Creatinine ratio is within the normal range. This result would prompt a discussion with a doctor about monitoring and managing potential CKD risk factors.
Example 2: Young Female with Normal Lab Values
- Inputs: Serum Creatinine: 0.8 mg/dL, BUN: 15 mg/dL, Age: 35, Sex: Female
- eGFR Calculation: The calculator yields an eGFR of approximately 105 mL/min/1.73m².
- BUN:Creatinine Ratio: 15 / 0.8 ≈ 18.8:1.
- Interpretation: The eGFR is well above 90, indicating normal kidney function (Stage G1). The BUN:Creatinine ratio is also normal. These results suggest healthy kidney function. A reliable eGFR calculator using creatinine and urea provides this peace of mind.
How to Use This eGFR Calculator using Creatinine and Urea
- Enter Serum Creatinine: Input the creatinine value from your lab report. Make sure to select the correct unit (mg/dL or µmol/L). The calculator will handle the conversion.
- Enter Blood Urea Nitrogen (BUN): Input your BUN or Urea value and its corresponding unit. This is used for the secondary ratio calculation.
- Enter Your Age: Provide your age in years.
- Select Your Sex: Choose ‘Male’ or ‘Female’ from the dropdown. This is crucial as the formula constants differ.
- Review Your Results: The calculator automatically updates. The primary result is your eGFR. You will also see your calculated CKD stage and BUN:Creatinine ratio, providing a complete picture. The chart and table will highlight your current standing.
Interpreting the results involves checking the eGFR value against the CKD stages table. An eGFR below 60 for three months or more may indicate chronic kidney disease. Always discuss your results with a healthcare professional for proper diagnosis and guidance. Using an eGFR calculator using creatinine and urea is the first step in managing kidney health proactively.
Key Factors That Affect eGFR Results
Several factors can influence your eGFR and the health of your kidneys. Understanding these is vital for accurate interpretation.
- Age: Kidney function naturally declines with age. The formula accounts for this gradual decrease.
- Muscle Mass: Creatinine is a byproduct of muscle metabolism. Individuals with very high (e.g., bodybuilders) or very low (e.g., amputees, frail elderly) muscle mass may have creatinine levels that don’t accurately reflect their kidney function. This is a limitation of any creatinine-based eGFR calculator using creatinine and urea.
- Diet: A diet very high in protein (especially cooked meat) can temporarily increase creatinine levels. Dehydration can also concentrate both BUN and creatinine, leading to a temporarily lower eGFR and a high BUN:Creatinine ratio.
- Diabetes: Uncontrolled blood sugar is a leading cause of kidney damage. Effective diabetes management is crucial for preserving kidney function.
- High Blood Pressure (Hypertension): High blood pressure can damage the small blood vessels in the kidneys, impairing their function over time. It is a major risk factor for CKD.
- Medications: Certain drugs, including some antibiotics, diuretics, and nonsteroidal anti-inflammatory drugs (NSAIDs), can affect kidney function or interfere with the measurement of creatinine.
For more personalized advice, consult resources like the Kidney Health Diet Plan.
Frequently Asked Questions (FAQ)
1. What is a normal eGFR?
A normal eGFR is typically 90 mL/min/1.73m² or higher. However, values can decrease with age, so an eGFR between 60-89 might be considered normal in older adults without other signs of kidney damage.
2. Can my eGFR improve?
If a low eGFR is due to an acute kidney injury (AKI), such as from dehydration or a medication, it can often improve once the underlying cause is treated. For chronic kidney disease (CKD), the damage is generally permanent, but lifestyle changes and medical treatment can slow or halt further decline. Check out our guide on Slowing CKD Progression.
3. Why does this eGFR calculator use creatinine and urea?
The primary calculation for eGFR uses creatinine. We include urea (BUN) to calculate the BUN:Creatinine ratio, an important secondary metric that helps doctors diagnose the *cause* of kidney problems, such as distinguishing between dehydration (prerenal) and direct kidney damage (renal).
4. How often should I check my eGFR?
The frequency depends on your CKD stage and risk factors. Your doctor might recommend testing annually, semi-annually, or more often if your kidney function is changing rapidly or you are starting a new treatment.
5. Why was ‘race’ removed from the eGFR calculation?
The 2021 CKD-EPI equation removed the race modifier because it was a social construct, not a biological one. Its inclusion was found to systematically overestimate kidney function in Black patients, potentially delaying diagnosis and treatment. This eGFR calculator using creatinine and urea uses the modern, more equitable formula.
6. What does a high BUN:Creatinine ratio mean?
A ratio above 20:1 can suggest “prerenal” causes of kidney dysfunction, meaning the problem originates before the kidneys. Common causes include dehydration, congestive heart failure, or increased protein breakdown. A lower ratio can sometimes indicate liver disease or a low-protein diet.
7. Is this calculator a substitute for medical advice?
No. This eGFR calculator using creatinine and urea is an informational tool. It is not a substitute for a professional medical diagnosis. Always consult with a qualified healthcare provider for any health concerns. You can find a specialist through our Nephrologist Directory.
8. What do the different units (mg/dL vs µmol/L) mean?
These are just different units of measurement for the same substances. The United States typically uses mg/dL, while much of the rest of the world uses µmol/L for creatinine and mmol/L for urea. Our calculator can use either, as long as you select the correct unit.