1. What is GFR Calculated from Cystatin C

GFR calculated from cystatin C using the CKD-EPI 2012 equation provides an alternative method for estimating glomerular filtration rate. Cystatin C is a protein produced by all nucleated cells and is filtered by the kidneys, making it a reliable marker for kidney function assessment.

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: This equation estimates GFR based on cystatin C levels, which is less influenced by muscle mass, diet, and other factors that affect creatinine-based calculations.

3. Importance of Cystatin C-Based GFR

Details: Cystatin C-based GFR estimation is particularly useful when creatinine-based estimates may be unreliable, such as in elderly patients, those with reduced muscle mass, or when more precise kidney function assessment is needed.

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, providing a more accurate GFR estimate in certain populations.

Q2: When is cystatin C particularly useful?
A: In elderly patients, those with extremes of muscle mass, malnutrition, paralysis, or amputations where creatinine may be misleading.

Q3: What are normal cystatin C values?
A: Normal serum cystatin C levels are typically 0.5-1.0 mg/L in healthy adults.

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 markers may provide the most accurate GFR estimation in many cases.