eGFR Calculator MSD Manual

CKD-EPI Creatinine-Cystatin C 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):

Unit Converter ▲

Unit Converter ▼

From:	To:

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

The CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) creatinine-cystatin C equation estimates glomerular filtration rate (GFR) from both serum creatinine and serum cystatin C, along with age and sex. This combined equation provides superior accuracy compared to equations using either biomarker alone and does not include race as a variable.

2. How Does The Calculator Work?

The calculator uses the CKD-EPI creatinine-cystatin C 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 a more accurate estimate of kidney function across diverse populations without race adjustment.

3. Importance Of eGFR Calculation

Details: Accurate GFR estimation using both creatinine and cystatin C is essential for precise diagnosis of chronic kidney disease, risk stratification, and guiding clinical decisions regarding medication dosing and referral to nephrology.

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 The Combined Creatinine-Cystatin C Equation?
A: The combined equation provides superior accuracy compared to equations using either biomarker alone and eliminates the need for race adjustment, making it more equitable across diverse populations.

Q2: What Are Normal eGFR Values?
A: Normal is generally ≥90 mL/min/1.73m², though values decline with age. Below 60 for 3+ months indicates chronic kidney disease.

Q3: When Should Creatinine And Cystatin C Be Measured?
A: Morning fasting samples are ideal for both biomarkers. Avoid testing after meat-heavy meals or vigorous exercise for creatinine measurement.

Q4: Are There Limitations To This Equation?
A: The equation may be less accurate in extremes of age and body composition, amputees, pregnant women, and those with rapidly changing kidney function or certain medical conditions affecting non-GFR determinants of creatinine or cystatin C.

Q5: Should This Be Used For Drug Dosing?
A: For precise drug dosing in critical situations, measured GFR (e.g., via iohexol clearance) may be needed, especially in populations where estimating equations are known to be less accurate.