Hepatology
FIB-4 Index
Non-invasive estimate of liver fibrosis.
Education and reference only. Not a substitute for clinical judgement, local policy or product labelling. Always verify before clinical use. Values are calculated in your browser and never stored.
Background
The FIB-4 index is a simple, non-invasive estimate of liver fibrosis calculated from four routinely available values: age, AST, ALT and platelet count. It was originally developed in HIV/hepatitis C co-infection but is now widely used as a first-line screen for advanced fibrosis in non-alcoholic fatty liver disease (NAFLD) and other chronic liver conditions. By combining liver enzyme levels with platelet count and age, it provides a quick way to identify who is unlikely to have advanced fibrosis and who needs further assessment.
Interpreting the result
A FIB-4 below about 1.45 makes advanced fibrosis unlikely and supports reassurance or monitoring in primary care. A value between 1.45 and 3.25 is indeterminate and usually prompts further testing, such as transient elastography or specialist referral. A value above 3.25 suggests advanced fibrosis is likely and warrants specialist referral. The thresholds are intended to rule out advanced fibrosis efficiently rather than to confirm a precise stage.
Worked example
A 60-year-old with NAFLD has an AST of 50 U/L, an ALT of 40 U/L and a platelet count of 150 ×10⁹/L, giving a FIB-4 of roughly 2.5. This falls in the indeterminate band, so further assessment with elastography or referral is appropriate rather than reassurance.
Pearls / pitfalls
- FIB-4 is best at ruling out advanced fibrosis; a low value is reassuring, but a raised value needs confirmation rather than being diagnostic.
- Accuracy is reduced at the extremes of age — it can over-call fibrosis in older people and under-perform in those under 35 — so interpret with caution.
- Acute hepatitis, very abnormal enzymes or low platelets from other causes can distort the result.
- An indeterminate result is common and should prompt second-line testing such as transient elastography, not repeated FIB-4 alone.
Evidence & validation
Developed by Sterling and colleagues in HIV/HCV co-infection and subsequently validated for fibrosis assessment across chronic liver diseases. It is recommended in NAFLD pathways, including NICE and European and American liver-society guidance, as a first-line non-invasive test.
Frequently asked questions
What FIB-4 value rules out advanced fibrosis?
A value below about 1.45 makes advanced fibrosis unlikely and supports monitoring in primary care. Values above 3.25 suggest advanced fibrosis is likely and warrant specialist referral.
What does an indeterminate result mean?
A FIB-4 between 1.45 and 3.25 is neither low nor high enough to be conclusive. It usually prompts second-line testing such as transient elastography, or specialist referral, rather than reassurance.
Is FIB-4 accurate in older people?
Its accuracy falls at the extremes of age and it can over-estimate fibrosis in older adults. Some guidance suggests a higher lower-threshold above 65, so interpret results in the clinical context.
Can FIB-4 replace a liver biopsy?
It cannot give a precise fibrosis stage, but it reduces the need for invasive testing by identifying low-risk patients. Those with raised or indeterminate scores proceed to further non-invasive tests or, occasionally, biopsy.
When should I use FIB-4?
It is a first-line screen for advanced fibrosis, commonly in NAFLD, to decide who needs specialist assessment. It is not intended for acute hepatitis or where enzymes and platelets are abnormal for unrelated reasons.
References
- Sterling RK, Lissen E, Clumeck N, et al. Development of a simple noninvasive index to predict significant fibrosis in patients with HIV/HCV coinfection. Hepatology. 2006;43(6):1317–1325.
- NICE NG49: Non-alcoholic fatty liver disease (NAFLD): assessment and management. 2016.
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