1. What is the NKF Cystatin C GFR Calculator?

The NKF Cystatin C GFR Calculator uses the CKD-EPI 2012 equation to estimate glomerular filtration rate (GFR) from serum cystatin C, age, and sex. This method provides an alternative to creatinine-based equations and may be more accurate in certain populations.

2. How Does the Calculator Work?

The calculator uses the NKF Cystatin C equation:

Where:

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

Explanation: The equation accounts for the relationship between cystatin C levels and kidney function, with adjustments for age and gender.

3. Importance of Cystatin C GFR Calculation

Details: Cystatin C-based GFR estimation is particularly useful when creatinine-based estimates may be unreliable, such as in patients with reduced muscle mass, amputations, or unusual dietary patterns.

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 serum cystatin C levels are typically 0.5-1.0 mg/L in healthy adults.

Q3: When is cystatin C testing recommended?
A: Cystatin C is recommended when creatinine-based eGFR is questionable, in elderly patients, or those with extremes of muscle mass.

Q4: Are there limitations to cystatin C measurement?
A: Cystatin C can be affected by thyroid dysfunction, corticosteroid use, and inflammation.

Q5: Can cystatin C and creatinine be used together?
A: Yes, combined equations using both markers may provide the most accurate GFR estimation in some cases.