Calculation of GFR Using Creatinine

CKD-EPI 2021 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 CKD-EPI 2021 Creatinine Equation?

The CKD-EPI 2021 (Chronic Kidney Disease Epidemiology Collaboration 2021) equation estimates glomerular filtration rate (GFR) from serum creatinine, age, and sex. This updated version provides improved accuracy in GFR estimation compared to previous equations.

2. How Does the Calculator Work?

The calculator uses the CKD-EPI 2021 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 non-linear relationship between creatinine and GFR, with updated coefficients for improved accuracy across different demographic groups.

3. Importance of GFR Calculation

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

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). The calculator provides eGFR in mL/min/1.73m².

5. Frequently Asked Questions (FAQ)

Q1: What's new in the CKD-EPI 2021 equation?
A: The 2021 version features updated coefficients and improved calibration, providing more accurate GFR estimates across diverse populations compared to the 2009 version.

Q2: What are the reference ranges for eGFR?
A: Normal eGFR is typically ≥90 mL/min/1.73m². Values between 60-89 may indicate mild reduction, while values below 60 sustained for 3+ months suggest 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 immediately after high-protein meals or intense physical activity.

Q4: What are the limitations of this equation?
A: Accuracy may be reduced in extreme age groups, individuals with unusual muscle mass, amputees, pregnant women, and patients with rapidly changing kidney function.

Q5: Can this equation be used for all clinical decisions?
A: While useful for screening and monitoring, critical decisions like drug dosing adjustments may require measured GFR in specific clinical situations.