National Kidney Foundation eGFR Calculator

NKF 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 NKF eGFR Calculator?

The National Kidney Foundation eGFR calculator estimates glomerular filtration rate (GFR) from serum creatinine, age, and sex. This equation provides an accurate assessment of kidney function and is widely used in clinical practice for evaluating renal health.

2. How Does the Calculator Work?

The calculator uses the NKF 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 to provide more accurate kidney function estimation.

3. Importance of eGFR Calculation

Details: Accurate GFR estimation is essential for diagnosing chronic kidney disease, determining disease stage, monitoring disease progression, and guiding appropriate medication dosing for patients with renal impairment.

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). For most accurate results, use fasting serum creatinine levels.

5. Frequently Asked Questions (FAQ)

Q1: What makes the NKF equation different from other eGFR equations?
A: The NKF equation uses optimized coefficients and exponents to provide more accurate GFR estimation across a wider range of kidney function levels, particularly in early-stage kidney disease.

Q2: What are the normal eGFR ranges?
A: Normal eGFR is generally ≥90 mL/min/1.73m². Values between 60-89 may indicate mildly reduced kidney function, while values below 60 for 3+ months typically indicate chronic kidney disease.

Q3: When is the best time to measure serum creatinine?
A: Morning fasting samples are preferred, but random samples can be used. Avoid testing immediately after high-protein meals or strenuous physical activity, as these can temporarily elevate creatinine levels.

Q4: Are there limitations to using 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 or muscle mass.

Q5: Can this calculator be used for medication dosing adjustments?
A: While useful for screening and monitoring, for precise drug dosing in critical situations, measured GFR (such as via iohexol or inulin clearance) may be necessary for optimal accuracy.