eGFR Calculator Creatinine Cystatin C

Combined Creatinine-Cystatin C CKD-EPI 2021 Equation:

\[ eGFR = 135 \times \min(Scr/\kappa, 1)^\alpha \times \max(Scr/\kappa, 1)^{-0.544} \times \min(Scys/0.8, 1)^{-0.323} \times \max(Scys/0.8, 1)^{-0.778} \times 0.9961^{age} \times (0.963 \text{ if female}) \]

Serum Creatinine (Scr):

mg/dL

Serum Cystatin C (Scys):

mg/L

Age:

years

Gender:

Estimated GFR (eGFR):

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1. What Is The Combined Creatinine-Cystatin C CKD-EPI 2021 Equation?

The CKD-EPI 2021 combined creatinine-cystatin C equation estimates glomerular filtration rate (GFR) using both serum creatinine and serum cystatin C biomarkers, along with age and sex. This combined approach provides superior accuracy compared to equations using either biomarker alone.

2. How Does The Calculator Work?

The calculator uses the CKD-EPI 2021 combined equation:

Where:

\( Scr \) — Serum creatinine (mg/dL)
\( Scys \) — Serum cystatin C (mg/L)
\( \kappa \) — 0.7 (female) or 0.9 (male)
\( \alpha \) — -0.219 (female) or -0.144 (male)
\( age \) — Age in years
0.963 — Female multiplier

Explanation: This equation combines the advantages of both creatinine and cystatin C biomarkers, providing more accurate GFR estimation across diverse populations and clinical scenarios.

3. Importance Of eGFR Calculation

Details: Accurate GFR estimation using combined biomarkers is essential for precise diagnosis and staging of chronic kidney disease, particularly in populations where creatinine-based equations may be less reliable.

4. Using The Calculator

Tips: Enter serum creatinine in mg/dL, serum cystatin C in mg/L, age in years, and select gender. All values must be valid (creatinine > 0, cystatin C > 0, age between 1-120).

5. Frequently Asked Questions (FAQ)

Q1: Why Use Combined Creatinine-Cystatin C Equation?
A: The combined equation provides superior accuracy compared to either biomarker alone, especially in elderly populations, extremes of body composition, and when muscle mass is abnormal.

Q2: What Are The Advantages Over Creatinine-Only Equations?
A: Cystatin C is less affected by muscle mass, diet, and race, making the combined equation more reliable across diverse patient populations.

Q3: When Should Combined Equation Be Used?
A: Recommended when precise GFR estimation is critical, in research settings, for drug dosing decisions, and when creatinine-based estimates are questionable.

Q4: Are There Limitations To This Equation?
A: Requires measurement of both biomarkers, which may increase cost. Less validated in specific populations like pregnant women, amputees, and those with rapidly changing kidney function.

Q5: How Does This Compare To Other Equations?
A: The 2021 CKD-EPI combined equation represents the most recent and accurate method for GFR estimation using commonly available biomarkers.