Calculation of eGFR from Serum Creatinine

eGFR Equation:

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

Estimated GFR (eGFR):

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1. What is the eGFR Calculation from Serum Creatinine?

This equation estimates glomerular filtration rate (GFR) from serum creatinine, age, and sex. It provides an accurate assessment of kidney function based on serum creatinine levels and demographic factors.

2. How Does the Calculator Work?

The calculator uses the eGFR equation:

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

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 and GFR, with different coefficients for different demographic groups.

3. Importance of eGFR Calculation

Details: Accurate GFR estimation is crucial for diagnosing chronic kidney disease, determining disease stage, monitoring kidney function over time, and guiding appropriate medication dosing for renal clearance.

4. Using the Calculator

Tips: Enter serum creatinine in mg/dL, age in years, and select gender. All values must be valid (creatinine > 0, age between 1-120 years). Use fasting serum creatinine values for most accurate results.

5. Frequently Asked Questions (FAQ)

Q1: What is the source of this equation?
A: This equation is derived from population studies correlating serum creatinine levels with measured glomerular filtration rates.

Q2: What are normal eGFR values?
A: Normal eGFR is generally ≥90 mL/min/1.73m², though values naturally decline with advancing age. Values below 60 mL/min/1.73m² persisting for 3+ months indicate chronic kidney disease.

Q3: When is the best time to measure serum creatinine?
A: Morning fasting samples are ideal, but random samples are acceptable for clinical use. Avoid testing immediately after meat-heavy meals or vigorous exercise.

Q4: Are there limitations to this equation?
A: The equation may be less accurate in extremes of age and body composition, amputees, pregnant women, and individuals with rapidly changing kidney function or unusual muscle mass.

Q5: Can this equation be used for medication dosing?
A: While useful for estimating kidney function, for precise drug dosing in critical situations, measured GFR (e.g., via iohexol or inulin clearance) may be required.