Gfr Calculator

The GFR (Glomerular Filtration Rate) Calculator is an essential tool used by healthcare providers and patients alike to evaluate kidney function. GFR measures how well your kidneys filter blood, removing waste and excess fluids. Monitoring GFR helps detect kidney disease early, guide treatment, and track kidney health over time.

GFR (MDRD) Calculator
mg/dL
years
MDRD 4-variable formula, units: mg/dL, age ≥ 18.
More info

How to Use the GFR Calculator

To use the GFR Calculator:

  1. Enter Serum Creatinine Level – Input the serum creatinine from your blood test, in mg/dL or µmol/L.
  2. Provide Age – Your age in years.
  3. Select Sex – Male or Female.
  4. Select Race – Choose the appropriate category if available (e.g., Black or Non-Black).
  5. Click Calculate – The calculator will provide your estimated GFR in mL/min/1.73 m².

Ensure units for serum creatinine match the calculator input.

GFR Calculation Formulas

Several formulas exist to estimate GFR, with the most common being:

1. CKD-EPI Equation

Widely used due to improved accuracy across populations. The formula: GFR=141×min⁡(Scrκ,1)α×max⁡(Scrκ,1)−1.209×0.993Age×Race and Sex FactorGFR = 141 \times \min\left(\frac{S_{cr}}{\kappa}, 1\right)^{\alpha} \times \max\left(\frac{S_{cr}}{\kappa}, 1\right)^{-1.209} \times 0.993^{\text{Age}} \times \text{Race and Sex Factor}GFR=141×min(κScr​​,1)α×max(κScr​​,1)−1.209×0.993Age×Race and Sex Factor

Where:

  • ScrS_{cr}Scr​ = Serum creatinine
  • κ\kappaκ = 0.7 for females, 0.9 for males
  • α\alphaα = -0.329 for females, -0.411 for males
  • Race factor = 1.159 for Black, 1 for others
  • Age in years

2. MDRD Equation

Another commonly used formula: GFR=175×(Scr)−1.154×(Age)−0.203×(0.742 if female)×(1.212 if Black)GFR = 175 \times (S_{cr})^{-1.154} \times (\text{Age})^{-0.203} \times (0.742 \text{ if female}) \times (1.212 \text{ if Black})GFR=175×(Scr​)−1.154×(Age)−0.203×(0.742 if female)×(1.212 if Black)

Example of GFR Calculation

Example:

  • Serum Creatinine: 1.0 mg/dL
  • Age: 45 years
  • Sex: Male
  • Race: Non-Black

Using CKD-EPI:

  • κ=0.9\kappa = 0.9κ=0.9, α=−0.411\alpha = -0.411α=−0.411
  • Scrκ=1.00.9=1.11\frac{S_{cr}}{\kappa} = \frac{1.0}{0.9} = 1.11κScr​​=0.91.0​=1.11
  • min⁡(1.11,1)=1\min(1.11, 1) = 1min(1.11,1)=1, max⁡(1.11,1)=1.11\max(1.11, 1) = 1.11max(1.11,1)=1.11
  • 1α=11^{\alpha} = 11α=1, 1.11−1.209≈0.8761.11^{-1.209} \approx 0.8761.11−1.209≈0.876
  • 0.99345≈0.7160.993^{45} \approx 0.7160.99345≈0.716

Calculation: GFR=141×1×0.876×0.716×1=141×0.627=88.4 mL/min/1.73 m2GFR = 141 \times 1 \times 0.876 \times 0.716 \times 1 = 141 \times 0.627 = 88.4 \text{ mL/min/1.73 m}^2GFR=141×1×0.876×0.716×1=141×0.627=88.4 mL/min/1.73 m2

Understanding GFR Results

  • 90+ mL/min/1.73 m²: Normal kidney function
  • 60–89: Mild decrease, possibly normal in elderly
  • 45–59: Mild to moderate decrease (CKD stage 3a)
  • 30–44: Moderate to severe decrease (CKD stage 3b)
  • 15–29: Severe decrease (CKD stage 4)
  • <15: Kidney failure (CKD stage 5)

If your GFR is low, consult a healthcare provider for further evaluation.

Additional Insights on GFR

  • GFR helps diagnose chronic kidney disease (CKD) early.
  • It considers factors affecting creatinine like muscle mass, age, and race.
  • GFR estimates are used to adjust medication dosages.
  • Regular monitoring is key if you have risk factors like diabetes or hypertension.
  • GFR is a better measure of kidney function than serum creatinine alone.

20 Frequently Asked Questions (FAQs)

1. What is GFR?
Glomerular Filtration Rate, measuring how well kidneys filter blood.

2. How is GFR estimated?
Using blood creatinine levels, age, sex, and race in formulas.

3. Why does race affect GFR?
Differences in muscle mass influence creatinine levels.

4. Can I calculate GFR at home?
Yes, with lab results and a calculator, but consult a doctor for interpretation.

5. What does a low GFR mean?
Possible kidney impairment or disease.

6. Is a high GFR good?
Generally yes, indicates healthy kidneys.

7. How often should GFR be tested?
Depends on health status; often annually for at-risk patients.

8. Does hydration affect GFR?
Yes, dehydration can temporarily affect creatinine and GFR.

9. Can medications affect GFR results?
Yes, some drugs impact kidney function and test results.

10. What is a normal GFR range?
Typically 90 mL/min/1.73 m² or higher.

11. Can children use the same GFR calculator?
No, pediatric formulas differ.

12. How is GFR different from creatinine clearance?
Creatinine clearance uses urine tests; GFR is estimated from blood tests.

13. Does muscle mass affect GFR?
Yes, more muscle usually means higher creatinine.

14. Is GFR reliable for all populations?
It’s an estimate and may vary in some groups.

15. Can kidney disease be reversed if caught early?
Sometimes, with lifestyle and medical intervention.

16. What factors lower GFR?
Kidney damage, age, dehydration, some diseases.

17. What does mL/min/1.73 m² mean?
It’s filtration rate adjusted for average body surface area.

18. Can I rely solely on GFR for kidney health?
No, it should be part of a full clinical evaluation.

19. What is CKD?
Chronic Kidney Disease, progressive loss of kidney function.

20. When should I see a doctor about GFR results?
If GFR is consistently below 60 or you have symptoms.