🧬 Liver Fibrosis FIB-4 Index Calculator
What the FIB-4 index is
FIB-4 is a simple score that estimates the chance of advanced liver scarring (fibrosis stage F3–F4) from four values that appear on routine blood tests: age, AST, ALT and platelet count. It was first described in 2006 for people with HIV and hepatitis C, and is now widely used as the first screening step for fatty liver disease (MASLD, formerly NAFLD).
The formula is: FIB-4 = (age × AST) ÷ (platelets × √ALT), with AST and ALT in U/L and platelets in 109/L.
How to enter your values
- AST and ALT: use the numbers from the same blood test, in U/L (IU/L is the same).
- Platelets: 109/L and 103/µL (thousands per microlitre) give the same number, for example 250. If your report shows 250,000/µL, enter 250.
How the result is read
This calculator uses the cut-offs recommended for fatty liver disease (MASLD) by the American Association for the Study of Liver Diseases:
- Below 1.30: low risk. Advanced fibrosis is unlikely; FIB-4 is good at ruling it out. For people aged 65 and over, a cut-off of 2.0 is used instead, because the score rises naturally with age.
- 1.30 to 2.67: indeterminate. Guidelines suggest a second test, usually liver stiffness measurement (FibroScan) or an ELF blood test.
- 2.67 or higher: higher risk. Usually leads to referral to a liver specialist.
For chronic hepatitis C and HIV, the original study used 1.45 and 3.25 as the lower and upper cut-offs. Your doctor will choose the cut-off that fits your condition.
Limits of FIB-4
- It is less reliable under age 35, and it can be falsely high in people over 65.
- Sudden liver inflammation (acute hepatitis, a recent heavy drinking episode, some medicines) raises AST and ALT and can distort the score.
- Low platelets from causes other than liver disease also raise the score.
- FIB-4 is a screening estimate, not a diagnosis. Only your doctor can interpret it alongside your history, scans and other tests.
Educational estimate only. Please discuss your result with your doctor.