How to Calculate GFR Value

GFR Calculation Formula:

\[ eGFR = 142 \times \min(Scr/\kappa, 1)^\alpha \times \max(Scr/\kappa, 1)^{-1.200} \times 0.9938^{age} \times (1.012 \text{ if female}) \]

Estimated GFR (eGFR):

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1. What is GFR Calculation?

GFR (Glomerular Filtration Rate) calculation estimates kidney function by measuring how much blood passes through the glomeruli each minute. This equation provides an accurate assessment of renal function based on serum creatinine levels, age, and gender.

2. How Does the Calculator Work?

The calculator uses the GFR calculation formula:

\[ eGFR = 142 \times \min(Scr/\kappa, 1)^\alpha \times \max(Scr/\kappa, 1)^{-1.200} \times 0.9938^{age} \times (1.012 \text{ if female}) \]

Where:

\( Scr \) — Serum creatinine (mg/dL)
\( \kappa \) — 0.7 (female) or 0.9 (male)
\( \alpha \) — -0.241 (female) or -0.302 (male)
\( age \) — Age in years
1.012 — Female multiplier

Explanation: The equation accounts for the non-linear relationship between creatinine levels and glomerular filtration rate, with specific coefficients optimized for different demographic characteristics.

3. Importance of GFR Calculation

Details: Accurate GFR estimation is essential for evaluating kidney health, detecting early-stage chronic kidney disease, monitoring disease progression, and determining appropriate medication dosages for patients with renal impairment.

4. Using the Calculator

Tips: Enter serum creatinine in mg/dL, age in years, and select gender. Ensure all values are valid (creatinine > 0, age between 1-120 years). For optimal accuracy, use fasting serum creatinine measurements.

5. Frequently Asked Questions (FAQ)

Q1: What is the normal range for GFR?
A: Normal GFR is generally ≥90 mL/min/1.73m². Values between 60-89 may indicate mild kidney impairment, while values below 60 for three months or more suggest chronic kidney disease.

Q2: How often should GFR be calculated?
A: Frequency depends on individual risk factors. High-risk patients (diabetes, hypertension) should be tested annually, while those with established kidney disease may need more frequent monitoring.

Q3: What factors can affect GFR accuracy?
A: Muscle mass, diet (especially protein intake), hydration status, certain medications, and recent exercise can influence serum creatinine levels and thus GFR calculations.

Q4: Are there limitations to this equation?
A: This equation may be less accurate in elderly patients, those with extreme body weights, amputees, pregnant women, and individuals with rapidly changing kidney function.

Q5: Can this calculator be used for children?
A: No, this equation is validated for adults only. Pediatric GFR calculations require different equations that account for body surface area and developmental stages.