1. What is the Cystatin C CKD-EPI 2012 Equation?

The Cystatin C CKD-EPI 2012 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, particularly those with reduced muscle mass.

2. How Does the Calculator Work?

The calculator uses the Cystatin C CKD-EPI 2012 equation:

Where:

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

Explanation: The equation uses cystatin C concentration to estimate GFR, with adjustments for age and gender. Cystatin C is less influenced by muscle mass than creatinine.

3. Importance of Cystatin C eGFR Calculation

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

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 race, making it more reliable in elderly, malnourished, or amputee patients.

Q2: When is cystatin C particularly useful?
A: In patients with reduced muscle mass, obesity, liver disease, or when creatinine-based eGFR is inconsistent with clinical findings.

Q3: Are there limitations to cystatin C measurement?
A: Cystatin C can be affected by thyroid dysfunction, corticosteroid use, and inflammation. It's also more expensive than creatinine testing.

Q4: Can cystatin C and creatinine be combined?
A: Yes, there are equations that combine both biomarkers (CKD-EPI creatinine-cystatin C equation) for even more accurate GFR estimation.

Q5: What are normal cystatin C values?
A: Normal serum cystatin C is typically 0.5-1.0 mg/L in healthy adults, though reference ranges may vary by laboratory.