GFR Calculator National Kidney Foundation

NKF GFR 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 NKF GFR Equation?

The National Kidney Foundation (NKF) GFR equation estimates glomerular filtration rate (GFR) from serum creatinine, age, and sex. This equation provides a standardized method for assessing kidney function and is widely used in clinical practice.

2. How Does the Calculator Work?

The calculator uses the NKF GFR 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 GFR Calculation

Details: Accurate GFR estimation is essential for diagnosing kidney disease, determining disease stage, monitoring progression, and guiding appropriate treatment decisions and medication dosing.

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).

5. Frequently Asked Questions (FAQ)

Q1: What is the difference between NKF and CKD-EPI equations?
A: The NKF equation uses slightly different coefficients (142 vs 141, different exponents) and is optimized for specific patient populations.

Q2: What are the normal GFR ranges?
A: Normal GFR is generally ≥90 mL/min/1.73m². Values below 60 mL/min/1.73m² for 3+ months indicate chronic kidney disease.

Q3: When is the best time to measure creatinine?
A: Morning fasting samples are preferred, but random samples are acceptable. Avoid testing after high-protein meals or intense physical activity.

Q4: Are there limitations to this equation?
A: The 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 medication dosing?
A: While useful for screening, precise drug dosing may require measured GFR in certain clinical situations or high-risk populations.