Cystatin C is made by all cells at a steady rate and is less affected by muscle mass than creatinine. KDIGO recommends confirming an eGFR of 45–59 with cystatin C, and using the combined equation when an accurate GFR matters, such as for drug dosing.
How to use the Glomerular Filtration Rate Calculator
- Sex
- Age
- Serum creatinine
- Cystatin C (0 if not measured)
Results update as you type, and every field accepts the units shown in its menu.
How it works
Enter creatinine and, if available, cystatin C. Leave cystatin C at zero to use creatinine alone.
GFR categories (KDIGO)
| Stage | eGFR (mL/min/1.73 m²) | Description |
|---|---|---|
| G1 | 90 or above | Normal or high |
| G2 | 60–89 | Mildly decreased |
| G3a | 45–59 | Mildly to moderately decreased |
| G3b | 30–44 | Moderately to severely decreased |
| G4 | 15–29 | Severely decreased |
| G5 | below 15 | Kidney failure |
Inputs explained
| Field | What to enter |
|---|---|
| Sex | Choose one: Male, Female |
| Age | In years |
| Serum creatinine | Units: mg/dL, µmol/L |
| Cystatin C (0 if not measured) | In mg/L |
Health note: this calculator is for education and screening only and is not a diagnosis or treatment advice. Discuss your results with a qualified clinician.
Formula
Creatinine: 142 × min(Scr/κ,1)^α × max(Scr/κ,1)^−1.200 × 0.9938^age (× 1.012 women)
Cystatin C (2012): 133 × min(Scys/0.8,1)^−0.499 × max(Scys/0.8,1)^−1.328 × 0.996^age (× 0.932 women)
Combined (2021): 135 × min(Scr/κ,1)^α × max(Scr/κ,1)^−0.544 × min(Scys/0.8,1)^−0.323 × max(Scys/0.8,1)^−0.778 × 0.9961^age (× 0.963 women); α = −0.219 (women) or −0.144 (men)
Worked example
Inputs — Sex: Male; Age: 60 years; Serum creatinine: 1.1 mg/dL; Cystatin C (0 if not measured): 1 mg/L.
Results — eGFR – creatinine = 77 mL/min/1.73 m²; eGFR – cystatin C = 78 mL/min/1.73 m²; eGFR – combined = 80 mL/min/1.73 m²; GFR category (combined) = G2 – mildly decreased.
Key terms
- Cystatin C
- A small protein filtered by the kidneys, used as a GFR marker.
Frequently asked questions
Why use cystatin C?
It is less affected by muscle mass, diet and race than creatinine.
Which eGFR should I trust?
The combined creatinine–cystatin C equation is the most accurate.
Is cystatin C affected by anything?
Thyroid disease, steroids, inflammation and obesity can raise it.