eGFR Calculator Cystatin

Cystatin C CKD-EPI 2012 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 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 marker 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:

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

Where:

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

Explanation: This equation uses cystatin C as the filtration marker, which is less influenced by muscle mass than creatinine, making it particularly useful in elderly patients and those with malnutrition.

3. Importance of Cystatin C eGFR Calculation

Details: Cystatin C-based eGFR provides an alternative assessment of kidney function that complements creatinine-based estimates. It's especially valuable when creatinine may be misleading due to extremes of muscle mass, amputation, or neuromuscular 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). Cystatin C should be measured using a standardized assay.

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, providing more accurate GFR estimation 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 estimates are questionable. Also useful for confirming CKD diagnosis.

Q3: Are there limitations to cystatin C measurement?
A: Cystatin C can be affected by thyroid dysfunction, corticosteroid use, and inflammation. Cost and availability may also be limitations.

Q4: How do cystatin C and creatinine eGFR compare?
A: Using both markers together provides the most accurate GFR estimation. Discordant results may indicate specific clinical conditions.

Q5: Is cystatin C affected by race?
A: Unlike creatinine-based equations, the cystatin C equation does not require race adjustment, as cystatin C levels show minimal racial variation.