Cystatin C Cr eGFR Calculator

Cystatin C and Cr eGFR 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 Cystatin C Cr eGFR Equation?

The Cystatin C and Creatinine eGFR equation combines both biomarkers to estimate glomerular filtration rate (GFR). This combined approach provides superior accuracy compared to equations using either marker alone, especially in populations where creatinine-based estimates may be unreliable.

2. How Does the Calculator Work?

The calculator uses the combined Cystatin C and Creatinine 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 incorporates both creatinine and cystatin C biomarkers, providing a more comprehensive assessment of kidney function by accounting for different physiological factors affecting each marker.

3. Importance of Combined Cystatin C and Creatinine eGFR

Details: The combined equation offers improved accuracy across diverse populations, reduced bias in special populations (elderly, obese, malnourished), and better correlation with measured GFR compared to single-marker equations.

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 combined cystatin C and creatinine instead of either alone?
A: Combined equations provide superior accuracy and precision, reduce misclassification, and perform better in populations where muscle mass or other factors may affect creatinine levels.

Q2: What are the advantages of cystatin C over creatinine?
A: Cystatin C is less affected by muscle mass, diet, and inflammation, making it more reliable in elderly, obese, or malnourished patients.

Q3: When is combined eGFR particularly useful?
A: In elderly patients, those with extremes of muscle mass, liver cirrhosis, vegetarian diets, or when creatinine-based estimates are discordant with clinical assessment.

Q4: Are there limitations to this equation?
A: Requires measurement of both biomarkers, increased cost, and may be less accurate in specific conditions like thyroid disorders or high-dose corticosteroid use.

Q5: How does this compare to CKD-EPI equations?
A: Combined equations generally show better performance characteristics and are recommended when highest accuracy is needed for clinical decision-making.