GFR Calculated From Cystatin C Low

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):

Unit Converter ▲

Unit Converter ▼

From:	To:

1. What is the Cystatin C Equation?

The Cystatin C equation estimates glomerular filtration rate (GFR) from serum cystatin C levels, age, and sex. Cystatin C is an alternative biomarker to creatinine that may provide more accurate GFR estimation in certain populations, particularly when muscle mass is abnormal.

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 GFR, with adjustments for age and gender differences in cystatin C production.

3. Importance of Cystatin C-Based GFR Calculation

Details: Cystatin C-based GFR estimation is particularly valuable in patients with abnormal muscle mass, malnutrition, obesity, or when creatinine-based estimates may be unreliable. It provides an alternative assessment of kidney function.

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: When should cystatin C be used instead of creatinine?
A: Cystatin C is preferred in patients with extremes of muscle mass, amputees, malnutrition, obesity, or when creatinine production is abnormal.

Q2: What are the advantages of cystatin C?
A: Cystatin C is less influenced by muscle mass, diet, and gender compared to creatinine, potentially providing more accurate GFR estimation.

Q3: 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.

Q4: Are there limitations to cystatin C measurement?
A: Cystatin C can be affected by thyroid dysfunction, corticosteroid use, inflammation, and some malignancies. Standardization between assays is improving but not perfect.

Q5: Can cystatin C and creatinine be combined?
A: Yes, combined equations using both biomarkers may provide the most accurate GFR estimation in many clinical situations.