FIB-4 Index Calculator
Estimate liver fibrosis risk with the non-invasive FIB-4 index from age, AST, ALT and platelet count — a first-line screen before elastography or biopsy.
How it works
FIB-4 = (age × AST) ÷ (platelets × √ALT) · <1.45 low, 1.45–3.25 indeterminate, >3.25 high risk of advanced fibrosis
FIB-4 combines age with two liver enzymes and the platelet count to estimate the likelihood of advanced fibrosis without a biopsy, which is why it is a recommended first step in fatty-liver and hepatitis pathways. Its strength is ruling fibrosis out: a value under 1.45 has a high negative predictive value, so most people below it can avoid further testing. The wide indeterminate band is its main limitation and is where elastography earns its place.
Worked example
For a 55-year-old with AST 40, ALT 45 and platelets 200: (55 × 40) ÷ (200 × √45) = 2200 ÷ (200 × 6.71) = 2200 ÷ 1341.6 ≈ 1.64 — the indeterminate band, where a follow-up test such as elastography is usually advised.
Frequently asked questions
What does a low FIB-4 tell me?
A value below 1.45 makes advanced liver fibrosis unlikely, so it is good at ruling it out. It does not exclude milder liver disease and does not replace clinical follow-up.
Why is the middle range so wide?
The 1.45–3.25 band is deliberately cautious: FIB-4 cannot confidently classify these patients, so guidelines send them for a more direct test like transient elastography (FibroScan) rather than guessing.
Does FIB-4 work at any age?
It is validated in adults and tends to over-call fibrosis in people over about 65, where some pathways raise the low cut-off to 2.0. It is not intended for children.
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Educational clinical estimate only — not a diagnosis, medical advice, or treatment. Scores are screening aids that must be interpreted by a qualified clinician alongside the full clinical picture. Never make care decisions from this tool alone.