What is the FIB-4 index?

FIB-4 is a non-invasive fibrosis score calculated from four routine lab values: age, AST, ALT, and platelet count. It was originally validated in HIV/HCV co-infected patients and is now widely used for chronic liver disease screening.

What do the FIB-4 cutoff values mean?

A score below 1.30 indicates low risk for advanced fibrosis (high negative predictive value). A score above 2.67 indicates high risk for advanced fibrosis (F3–F4). Values between 1.30 and 2.67 are indeterminate and may require additional testing such as elastography or biopsy.

What units should I use for platelet count?

Enter platelets in 10^9/L, which is the same as thousands per microliter (10^3/µL). For example, a count of 150,000/µL should be entered as 150.

Is the FIB-4 index a substitute for liver biopsy?

No. The FIB-4 index is a screening tool to estimate fibrosis risk, not a definitive diagnosis. Liver biopsy remains the gold standard. Always consult a qualified healthcare professional for medical decisions.

Can FIB-4 be used for all liver diseases?

FIB-4 was validated primarily for chronic hepatitis C and NAFLD. It may be less accurate in other conditions such as acute hepatitis, where AST and ALT can be transiently very high. Interpretation should always consider the clinical context.

Why does a higher platelet count lower the FIB-4 score?

Platelets decrease as liver fibrosis progresses because the scarred liver produces less thrombopoietin and portal hypertension causes platelet sequestration in the spleen. A lower platelet count therefore raises the FIB-4 score, reflecting worse fibrosis.

FIB-4 Index Calculator

Enter age, AST, ALT, and platelet count to calculate the FIB-4 index and assess your risk for advanced liver fibrosis.

Lab Values

Age (years)

AST (U/L)

Aspartate aminotransferase

ALT (U/L)

Alanine aminotransferase

Platelet Count (10⁹/L)

Enter in 10⁹/L (same as 10³/µL). Example: 150,000/µL = 150.

Enter lab values and click Calculate to see your FIB-4 score.

FIB-4 Index Score

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(Age × AST) / (Platelets × √ALT)

0 1.30 2.67 5+

Reference Ranges

FIB-4 Score	Risk Level	Interpretation
< 1.30	Low Risk	Advanced fibrosis unlikely (F0–F1)
1.30 – 2.67	Indeterminate	Further testing may be needed
> 2.67	High Risk	Advanced fibrosis likely (F3–F4)

Input Summary

Age

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AST

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ALT

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Platelets

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Medical Disclaimer: This tool is for educational reference only and is not a substitute for professional medical diagnosis, advice, or treatment. Always consult a qualified healthcare professional before making any clinical decisions.

Summary

The FIB-4 index is a non-invasive blood-based score used to estimate the degree of liver fibrosis in patients with chronic liver disease. It combines age, AST, ALT, and platelet count into a single number that correlates with liver biopsy findings. Scores below 1.30 suggest low fibrosis risk, scores above 2.67 suggest high risk for advanced fibrosis (F3–F4), and values in between are considered indeterminate.

How it works

Enter the patient's age in years.
Enter the AST (aspartate aminotransferase) level in U/L.
Enter the ALT (alanine aminotransferase) level in U/L.
Enter the platelet count in 10^9/L (or thousands per microliter).
The calculator applies the formula: FIB-4 = (Age × AST) / (Platelets × √ALT).
Your result is shown with a risk interpretation and reference ranges.

Use cases

Screen patients with chronic hepatitis B or C for significant liver fibrosis.
Monitor non-alcoholic fatty liver disease (NAFLD) progression over time.
Triage patients who may need a liver biopsy vs. those who can be monitored.
Track treatment response in patients on antiviral or metabolic therapy.
Assess fibrosis risk in patients with elevated liver enzymes of unknown cause.
Support clinical decision-making alongside imaging and biopsy findings.

Frequently Asked Questions

Last updated: 2026-09-30 · Reviewed by Nham Vu