1. What Is eGFR Calculated From Cystatin C?

eGFR calculated from cystatin C provides an alternative method for estimating glomerular filtration rate (GFR) that is less influenced by muscle mass, diet, and other non-renal factors compared to creatinine-based equations.

2. How Does The Calculator Work?

The calculator uses the cystatin C equation:

Where:

• \( Scys \) — Serum cystatin C (mg/L)
• \( 0.8 \) — Reference value for cystatin C
• \( -0.499 \) — Coefficient for the minimum part
• \( -1.328 \) — Coefficient for the maximum part
• \( age \) — 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.

3. Importance Of Cystatin C-Based eGFR

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 other non-renal factors, providing a more accurate GFR estimate in certain populations.

Q2: What are the advantages of cystatin C?
A: Better correlation with measured GFR, less variability, and more reliable in patients with abnormal muscle mass or nutritional status.

Q3: When is cystatin C particularly useful?
A: In elderly patients, those with malnutrition, amputees, bodybuilders, and patients with liver cirrhosis.

Q4: Are there limitations to cystatin C?
A: Cystatin C levels can be affected by thyroid dysfunction, glucocorticoid therapy, and inflammation.

Q5: Should both creatinine and cystatin C be measured?
A: In some cases, using both markers and averaging the results can provide the most accurate GFR estimation.