Cystatin C Based eGFR Calculation

Cystatin C Equation:

\[ eGFR = 133 \times \min(Scys/0.8, 1)^{-0.499} \times \max(Scys/0.8, 1)^{-1.328} \times 0.996^{Age} \times (0.932 \text{ if female}) \]

Estimated GFR (eGFR):

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1. What is the Cystatin C Based eGFR Calculation?

The Cystatin C based eGFR calculation estimates glomerular filtration rate (GFR) using serum cystatin C levels, age, and gender. Cystatin C is an alternative biomarker to creatinine that may provide more accurate GFR estimation in certain populations, particularly when muscle mass is abnormal.

2. How Does the Calculator Work?

The calculator uses the Cystatin C equation:

\[ eGFR = 133 \times \min(Scys/0.8, 1)^{-0.499} \times \max(Scys/0.8, 1)^{-1.328} \times 0.996^{Age} \times (0.932 \text{ if female}) \]

Where:

\( Scys \) — Serum cystatin C (mg/L)
\( Age \) — Age in years
0.932 — Female multiplier

Explanation: This equation accounts for the relationship between cystatin C levels and kidney function, with adjustments for age and gender differences in cystatin C production.

3. Importance of Cystatin C eGFR Calculation

Details: Cystatin C based eGFR is particularly valuable in patients where creatinine-based estimates may be unreliable, such as those with extremes of muscle mass, malnutrition, or neuromuscular diseases.

4. Using the Calculator

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

5. Frequently Asked Questions (FAQ)

Q1: Why use Cystatin C instead of creatinine?
A: Cystatin C is less affected by muscle mass, diet, and inflammation, making it more reliable in elderly, malnourished, or obese patients.

Q2: What are the advantages of Cystatin C eGFR?
A: Better correlation with measured GFR, less variability, and improved accuracy in detecting early kidney disease compared to creatinine-based equations.

Q3: When is Cystatin C testing recommended?
A: When creatinine-based eGFR is questionable, in patients with abnormal muscle mass, or when confirming CKD diagnosis is critical.

Q4: Are there limitations to Cystatin C measurement?
A: Cystatin C levels can be affected by thyroid dysfunction, corticosteroids, and some inflammatory conditions.

Q5: Can both creatinine and cystatin C be used together?
A: Yes, combined equations using both biomarkers often provide the most accurate GFR estimation and are recommended in specific clinical scenarios.