eGFR Cystatin C Calculation

Cystatin C Equation:

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

Estimated GFR (eGFR):

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1. What Is eGFR Cystatin C Calculation?

The eGFR Cystatin C calculation 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 altered muscle mass.

2. How Does The Calculator Work?

The calculator uses the 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 inverse relationship between cystatin C levels and glomerular filtration rate, with adjustments for age and gender differences in cystatin C production.

3. Importance Of eGFR Cystatin C Calculation

Details: Cystatin C-based eGFR is particularly valuable in patients where creatinine-based estimates may be unreliable, such as those with extremes of muscle mass, malnutrition, or neuromuscular diseases. It provides an alternative assessment of kidney function that is less influenced by non-renal factors.

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). Cystatin C levels are typically measured using standardized immunoassays.

5. Frequently Asked Questions (FAQ)

Q1: Why use cystatin C instead of creatinine for eGFR?
A: Cystatin C is less affected by muscle mass, diet, and inflammatory conditions, making it more reliable in elderly patients, those with malnutrition, or individuals with altered muscle composition.

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

Q3: When is cystatin C particularly useful?
A: Cystatin C is especially valuable in elderly patients, those with cirrhosis, amputees, bodybuilders, and patients with rapidly changing muscle mass where creatinine-based estimates may be misleading.

Q4: Are there limitations to cystatin C-based eGFR?
A: Cystatin C levels can be affected by thyroid dysfunction, corticosteroid use, and inflammatory conditions. It may also be more expensive to measure than creatinine.

Q5: Can cystatin C and creatinine be used together?
A: Yes, combined creatinine-cystatin C equations exist and may provide the most accurate GFR estimation in many clinical situations, particularly for confirming CKD diagnosis.