GFR Calculated from Cystatin C High

CKD-EPI 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 CKD-EPI Cystatin C Equation?

The CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) cystatin C equation estimates glomerular filtration rate (GFR) from serum cystatin C, age, and sex. Cystatin C is less influenced by muscle mass than creatinine, providing an alternative assessment of kidney function.

2. How Does the Calculator Work?

The calculator uses the CKD-EPI 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 specifically calculates high GFR values from cystatin C measurements using the CKD-EPI 2012 formula.

3. Importance of Cystatin C-Based GFR Calculation

Details: Cystatin C-based GFR estimation is particularly useful in patients with abnormal muscle mass, elderly individuals, and those where creatinine-based estimates may be unreliable. It provides complementary information to creatinine-based calculations.

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 age, making it more reliable in certain populations like the elderly, malnourished, or those with extreme muscle mass.

Q2: What are the advantages of cystatin C-based eGFR?
A: Better correlation with measured GFR, less variability, and improved accuracy in detecting early kidney function decline.

Q3: When should cystatin C be measured?
A: When creatinine-based estimates are questionable, in patients with abnormal muscle mass, or when more precise GFR estimation is needed.

Q4: Are there limitations to cystatin C measurement?
A: Cystatin C can be affected by thyroid dysfunction, corticosteroids, and inflammation. It's also more expensive than creatinine testing.

Q5: Can both creatinine and cystatin C be used together?
A: Yes, combining both markers in the CKD-EPI creatinine-cystatin C equation provides the most accurate GFR estimation.