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Fatty liver on a scan? Work out your FIB-4 score

An ultrasound shows fat in the liver but not scarring. FIB-4 is the first check guidelines recommend for scarring, and it needs only four numbers you probably already have: your age, two liver enzymes and your platelet count.

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Copy four numbers from your blood test report. The liver enzymes are often under "LFT" or "liver function", the platelets under "full blood count" or "CBC".

Age (years)Platelets

AST (also called SGOT)

ALT (also called SGPT)

U/L

What FIB-4 is, and where the numbers come from

FIB-4 (fibrosis-4) was developed in 2006 from people with HIV and hepatitis C and later checked in fatty liver disease. The formula is age × AST ÷ (platelets × √ALT). Scarring makes AST rise relative to ALT and makes platelets fall, and it becomes more common with age, so together they point to how much scarring (fibrosis) is likely.

Cut-offs: below 1.3, advanced fibrosis is unlikely; above 2.67, it is likely; in between, a second test is needed (Shah 2009). Because the score rises with age alone, a lower cut-off of 2.0 is used from 65 (McPherson 2017). The US liver society (AASLD 2023), the European guideline (EASL-EASD-EASO 2024) and NICE in the UK all start with FIB-4, and the American Diabetes Association advises it for adults with type 2 diabetes or prediabetes. The usual second test is elastography (FibroScan), or the ELF blood test.

Limits: FIB-4 is less accurate under 35, and it can mislead during a flare of hepatitis, after heavy drinking or when platelets are low for another reason. It estimates risk; it doesn't diagnose anything. Units: AST and ALT in U/L (the same number as IU/L; µkat/L is converted × 60), platelets in ×10⁹/L, which is the same number as ×10³/µL; Indian reports in lakh/mm³ are converted × 100.

General information, not medical advice. Your doctor will read your score alongside your history, other tests and a scan. If you have yellow eyes or skin, a swollen abdomen, vomiting blood or black stools, or confusion, get medical help straight away.