FIB-4 Calculator

Compute the Fibrosis-4 (FIB-4) index from your age, AST, ALT, and platelet count. FIB-4 is a published non-invasive score studied as a way to flag low versus higher likelihood of advanced liver fibrosis. This is an informational reference tool, not a diagnostic test.

Age

years

AST (aspartate aminotransferase)

U/L

ALT (alanine aminotransferase)

U/L

Platelet count

×10⁹/L

FIB-4 Index

FIB-4 is a published research score, not a diagnostic test. The cutoffs below come from Sterling et al. 2006. In adults over 65, the lower cutoff is less specific and a higher threshold (around 2.0) has been proposed. Only a clinician can interpret this in your full context.

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What FIB-4 Measures

The Fibrosis-4 index (FIB-4) is a non-invasive score that combines four values from routine blood work (your age, two liver enzymes, AST and ALT, and your platelet count) into a single number. It was first described by Sterling and colleagues in 2006 (Hepatology 43:1317–1325) in people with HIV/hepatitis C co-infection, and has since been studied widely in non-alcoholic fatty liver disease (NAFLD/MASLD), alcohol-related liver disease, and other chronic liver conditions as a way to estimate the likelihood of advanced fibrosis without a biopsy.

The logic behind it: as liver scarring (fibrosis) advances, AST tends to rise relative to ALT and the platelet count tends to fall, while older age independently raises fibrosis risk. FIB-4 packages these signals together. It is used in research and screening pathways as a first-pass filter, most reliably to rule out advanced fibrosis when the score is low.

Formula (Sterling et al., 2006):
FIB-4 = (Age × AST) ÷ (Platelets × √ALT)
Age in years, AST and ALT in U/L, platelet count in ×10⁹/L.

Published Reference Cutoffs

The table shows the cutoffs from the original Sterling 2006 validation. These are published research thresholds, not a diagnosis, and the intermediate band is explicitly indeterminate.

FIB-4 Score	Published interpretation (Sterling 2006)
Below 1.45	Low likelihood of advanced fibrosis (high negative predictive value to exclude stage 4–6)
1.45 – 3.25	Indeterminate zone: further assessment may be considered
Above 3.25	Higher likelihood of advanced fibrosis (specificity ~97% in the validation set)

Age over 65: FIB-4 was developed in middle-aged cohorts. In older adults the 1.45 lower cutoff loses specificity, and some NAFLD pathways use an age-adjusted lower threshold around 2.0 for people over 65 (McPherson et al., 2017). Discuss the right threshold for your age with your clinician.

Important Limitations

It is a screen, not a diagnosis. A high FIB-4 does not confirm fibrosis, and a low FIB-4 does not guarantee a healthy liver. Confirmation uses elastography (FibroScan), other validated panels, or biopsy, interpreted by a specialist.
Anything that moves AST, ALT, or platelets distorts it. Acute hepatitis, muscle injury (AST is also released from muscle), recent heavy exercise, alcohol, and conditions affecting platelet count can all push the score up or down independently of fibrosis.
Performance varies by population. Diagnostic accuracy differs between hepatitis C, NAFLD, and alcohol-related disease, and across ages.

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Frequently Asked Questions

What is the FIB-4 index?

FIB-4 (Fibrosis-4) is a non-invasive score that combines age, AST, ALT, and platelet count into a single number studied as a way to estimate the likelihood of advanced liver fibrosis. It was published by Sterling et al. in 2006 (Hepatology 43:1317-1325). It is a research and screening tool, not a diagnostic test, and is most reliable for ruling out advanced fibrosis when the score is low.

What is a normal FIB-4 score?

In the original Sterling 2006 validation, a FIB-4 below 1.45 indicated a low likelihood of advanced fibrosis (high negative predictive value), 1.45 to 3.25 was an indeterminate zone, and above 3.25 indicated a higher likelihood of advanced fibrosis. These are published research cutoffs, not a diagnosis. In adults over 65 the lower cutoff is less specific and a higher threshold around 2.0 has been proposed.

Does a high FIB-4 mean I have liver fibrosis?

No. A high FIB-4 raises the statistical likelihood of advanced fibrosis but does not confirm it. Many things other than fibrosis can raise AST or lower platelets, including acute hepatitis, muscle injury, alcohol, and other conditions. Confirmation requires elastography (FibroScan), other validated tests, or biopsy, interpreted by a specialist.

What units does the FIB-4 calculator use?

Age in years, AST and ALT in U/L (units per litre, the standard liver-enzyme unit on most lab reports), and platelet count in x10^9/L (also written as 10^9/L or thousands per microlitre, e.g. 250 x10^9/L = 250,000 per microlitre). Enter the platelet count as the number before the x10^9 (for example 250, not 250000).

Is FIB-4 the same as a FibroScan?

No. FIB-4 is a calculation from blood-test numbers; a FibroScan (transient elastography) is an ultrasound-based device that measures liver stiffness directly. They are often used together: FIB-4 as a low-cost first filter, then elastography or other tests for people who are not clearly in the low-risk band. Only a clinician can decide which tests you need.

Medical Disclaimer: The FIB-4 index is a published non-invasive research score, not a diagnostic test for liver fibrosis or cirrhosis. It cannot confirm or exclude liver disease on its own, and its accuracy varies by age and by the underlying liver condition. This tool is for general informational and educational use only. Cutoffs follow Sterling DR, et al. Hepatology. 2006;43(6):1317–1325. Always consult a qualified healthcare provider to interpret your liver-test results.

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