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 an alternative biomarker to creatinine that may provide more accurate GFR estimation in certain populations.

2. How Does the Calculator Work?

The calculator uses the CKD-EPI cystatin C equation:

Where:

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

Explanation: The equation uses cystatin C as the primary biomarker with adjustments for age and gender to estimate kidney function.

3. Importance of Cystatin C-Based GFR Calculation

Details: Cystatin C-based GFR estimation is particularly useful when creatinine-based estimates may be unreliable, such as in patients with reduced muscle mass, obesity, or unusual dietary patterns.

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 other non-renal factors, making it more reliable in certain patient populations.

Q2: What are the advantages of cystatin C?
A: Better correlation with measured GFR, less influenced by demographic factors, and more stable in patients with changing muscle mass.

Q3: When is cystatin C particularly useful?
A: In elderly patients, patients with malnutrition, amputees, bodybuilders, and those with rapidly changing muscle mass.

Q4: Are there limitations to cystatin C measurement?
A: Cystatin C can be affected by thyroid dysfunction, corticosteroid use, and inflammation in some cases.

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