eGFR Creatinine Cystatin C Calculation

eGFR Creatinine Cystatin C Equation:

\[ eGFR = 135 \times \min(Scr/\kappa, 1)^{\alpha} \times \max(Scr/\kappa, 1)^{-0.544} \times \min(Scys/0.8, 1)^{-0.323} \times \max(Scys/0.8, 1)^{-0.778} \times 0.9961^{Age} \times (0.963 \text{ if female}) \]

Serum Creatinine (Scr):

mg/dL

Serum Cystatin C (Scys):

mg/L

Age:

years

Gender:

Estimated GFR (eGFR):

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1. What is the eGFR Creatinine Cystatin C Equation?

The eGFR Creatinine Cystatin C equation estimates glomerular filtration rate (GFR) using both serum creatinine and serum cystatin C biomarkers, along with age and sex. This combined approach provides improved accuracy in assessing kidney function compared to equations using either biomarker alone.

2. How Does the Calculator Work?

The calculator uses the eGFR Creatinine Cystatin C equation:

Where:

\( Scr \) — Serum creatinine (mg/dL)
\( Scys \) — Serum cystatin C (mg/L)
\( \kappa \) — 0.7 (female) or 0.9 (male)
\( \alpha \) — -0.219 (female) or -0.144 (male)
\( Age \) — Age in years
0.963 — Female multiplier

Explanation: This equation combines the strengths of both creatinine and cystatin C biomarkers, accounting for their different relationships with GFR and providing more accurate estimates across diverse populations.

3. Importance of eGFR Calculation

Details: Accurate GFR estimation using both creatinine and cystatin C is particularly valuable for patients where creatinine-based estimates may be unreliable, such as those with muscle wasting, obesity, or unusual dietary patterns.

4. Using the Calculator

Tips: Enter serum creatinine in mg/dL, serum cystatin C in mg/L, age in years, and select gender. All values must be valid (creatinine > 0, cystatin C > 0, age between 1-120).

5. Frequently Asked Questions (FAQ)

Q1: Why use both creatinine and cystatin C?
A: Combining both biomarkers reduces bias and improves accuracy, as cystatin C is less affected by muscle mass and diet compared to creatinine.

Q2: What are the advantages over creatinine-only equations?
A: Better accuracy, especially in elderly patients, those with reduced muscle mass, and populations where creatinine production varies significantly.

Q3: When should cystatin C be measured?
A: Consider cystatin C testing when creatinine-based estimates are questionable, in elderly patients, or when precise GFR estimation is clinically important.

Q4: Are there limitations to this equation?
A: May be less accurate in extremes of age, pregnant women, and those with rapidly changing kidney function or certain medical conditions affecting cystatin C metabolism.

Q5: How does this compare to measured GFR?
A: The combined equation provides estimates closer to measured GFR than either biomarker alone, but direct measurement remains the gold standard for critical decisions.