Cystatin C Calculator GFR

Cystatin C GFR Calculator:

\[ eGFR = 133 \times \min(Scys/0.8, 1)^{-0.499} \times \max(Scys/0.8, 1)^{-1.328} \times 0.996^{Age} \times (0.932 \text{ if female}) \]

Estimated GFR (eGFR):

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1. What is the Cystatin C GFR Calculator?

The Cystatin C GFR calculator estimates glomerular filtration rate (GFR) using serum cystatin C levels, age, and gender. 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 CKD-EPI 2012 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 accounts for the relationship between cystatin C levels and kidney function, with adjustments for age and gender differences.

3. Importance of Cystatin C GFR Calculation

Details: Cystatin C-based GFR estimation is particularly valuable in patients where creatinine-based estimates may be unreliable, such as those with extremes of muscle mass, malnutrition, or liver disease.

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 influenced by muscle mass, diet, and other non-renal factors, making it more reliable in certain patient populations.

Q2: What are normal cystatin C values?
A: Normal cystatin C levels are typically 0.5-1.0 mg/L in healthy adults, though reference ranges may vary by laboratory.

Q3: When is cystatin C testing recommended?
A: Cystatin C is particularly useful in elderly patients, those with malnutrition, amputees, bodybuilders, and when creatinine-based estimates are questionable.

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

Q5: Can cystatin C and creatinine be used together?
A: Yes, combining both biomarkers in equations can provide the most accurate GFR estimation in many clinical situations.