How do I calculate the FIB-4 index?

By the formula: (age × AST) / (platelets × √ALT). You need four values: age, AST and ALT from biochemistry, and platelets from a complete blood count. The calculator computes it instantly and shows the risk zone.

What is a normal FIB-4?

An index below 1.45 is considered low risk of advanced fibrosis, above 3.25 high. The 1.45–3.25 range is an indeterminate "grey zone" where elastography (FibroScan) is needed. In people over 65 a lower threshold of 2.0 is sometimes used.

Does a high FIB-4 mean cirrhosis?

No, it is not a diagnosis. A high index only raises the likelihood of advanced fibrosis and means further work-up is needed — primarily elastography, sometimes biopsy. The final stage is determined by a hepatologist.

What distorts the index?

Acute hepatitis, a sharp rise in AST/ALT from other causes (for example muscle injury raises AST), and age: in the young under 35 the index may overestimate risk, in older adults the opposite. So FIB-4 is interpreted together with the clinical picture.

Do I need to take a special test?

No, FIB-4 is calculated from routine tests: biochemistry (AST, ALT) and a complete blood count (platelets). If you already have them, just enter the values. There is no separate "FIB-4 test" — it is a calculation.

FIB-4 calculator — liver fibrosis index

Enter your age and three lab values (AST, ALT, platelets) — the calculator computes the FIB-4 index. It is a simple way to estimate the likelihood of advanced liver fibrosis without a biopsy, from ordinary blood tests. FIB-4 does not replace a work-up but helps you see whether to go further.

Calculate FIB-4 index

Enter age, AST, ALT and platelets — the index appears instantly.

What the FIB-4 index means

Sterling thresholds. The index is less reliable in people under 35 and over 65.

FIB-4	Assessment
below 1.45	Low fibrosis risk
1.45–3.25	Indeterminate zone
above 3.25	Advanced fibrosis likely

What the FIB-4 index is

FIB-4 (Fibrosis-4) is a calculated index that estimates the likelihood of advanced liver fibrosis from four available parameters (age, AST, ALT and platelets). Fibrosis is scarring of liver tissue, the extreme stage of which is cirrhosis.

The value of FIB-4 is that it uses ordinary tests that are often already available, and helps screen out low-risk people without sending everyone for expensive investigations.

How it is calculated and interpreted

Formula: FIB-4 = (age × AST) / (platelets × √ALT). An index below 1.45 indicates a low probability of advanced fibrosis; above 3.25, a high one. The 1.45–3.25 range is a "grey zone" where further methods are needed, primarily elastography (FibroScan).

The thresholds are approximate and work less well in the young (under 35) and older adults (over 65) — in older people a higher lower threshold of 2.0 is sometimes used. Acute hepatitis and other causes of enzyme spikes distort the result.

Who benefits from FIB-4

Above all — in fatty liver disease (including non-alcoholic), chronic hepatitis, alcohol misuse, diabetes and metabolic syndrome. These are groups where fibrosis develops silently, and FIB-4 helps not to miss it.

If the index is high, the next step is not to panic but to see a doctor (hepatologist or gastroenterologist) for elastography and clarification. If you already have your labs, our service can read them in plain language.

Frequently asked questions

By the formula: (age × AST) / (platelets × √ALT). You need four values: age, AST and ALT from biochemistry, and platelets from a complete blood count. The calculator computes it instantly and shows the risk zone.
An index below 1.45 is considered low risk of advanced fibrosis, above 3.25 high. The 1.45–3.25 range is an indeterminate "grey zone" where elastography (FibroScan) is needed. In people over 65 a lower threshold of 2.0 is sometimes used.
No, it is not a diagnosis. A high index only raises the likelihood of advanced fibrosis and means further work-up is needed — primarily elastography, sometimes biopsy. The final stage is determined by a hepatologist.
Acute hepatitis, a sharp rise in AST/ALT from other causes (for example muscle injury raises AST), and age: in the young under 35 the index may overestimate risk, in older adults the opposite. So FIB-4 is interpreted together with the clinical picture.
No, FIB-4 is calculated from routine tests: biochemistry (AST, ALT) and a complete blood count (platelets). If you already have them, just enter the values. There is no separate "FIB-4 test" — it is a calculation.

Liver: bring the labs together

Upload your biochemistry and blood count — AI reviews AST, ALT, platelets and other liver markers and tells you what to do.

Decode my labs

This calculator is for informational reference and is not a diagnosis. The fibrosis stage is determined by elastography or biopsy and interpreted by a doctor.