What is the FIB-4 score?

FIB-4 is a non-invasive index that estimates liver fibrosis using four routine lab values: age, AST, ALT, and platelet count. It was originally validated in HIV/HCV coinfected patients and has since been widely adopted for NAFLD/NASH.

What are the FIB-4 cutoffs?

In the original validation: 2.67 suggests high risk of advanced fibrosis (F3–F4, ~80% PPV). Some guidelines use 3.25 for NAFLD-specific populations.

What units should I use for platelets?

Enter platelets in 10⁹/L (also reported as 10³/µL or k/µL). For example, a count of 200,000/µL should be entered as 200.

Is FIB-4 a replacement for liver biopsy?

No. FIB-4 is a screening tool, not a definitive diagnosis. It helps clinicians decide which patients are low-risk (and may not need a biopsy) versus those who warrant further evaluation with imaging or biopsy.

Who should not use FIB-4?

FIB-4 is less reliable in patients under 35 or over 65 years of age (age extremes can skew results), those with acute hepatitis, or conditions that independently raise AST (e.g., hemolysis, muscle disease). Always interpret in clinical context.

FIB-4 Fibrosis Index Calculator

Name: FIB-4 Fibrosis Index Calculator
Availability: InStock
Author: Nham Vu

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

Patient Lab Values

Age (years)

AST (U/L)

ALT (U/L)

Platelets (10⁹/L)

Enter as 10³/µL — e.g. 150,000/µL → 150

FIB-4 Interpretation Cutoffs

Score Interpretation

< 1.30 Low risk — advanced fibrosis unlikely

1.30 – 2.67 Indeterminate — further evaluation needed

> 2.67 High risk — advanced fibrosis likely

Cutoffs based on Sterling et al. (2006). NAFLD-specific guidelines may use <1.45 and >3.25.

Summary

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

How it works

Enter the patient's age in years.
Enter AST (aspartate aminotransferase) in U/L.
Enter ALT (alanine aminotransferase) in U/L.
Enter platelet count in 10⁹/L (or 10³/µL).
FIB-4 is computed as: (Age × AST) ÷ (Platelets × √ALT).
The result is compared against published cutoffs to classify fibrosis risk.

Use cases

Screen patients with NAFLD or NASH for advanced fibrosis without biopsy.
Monitor chronic hepatitis B or C patients for fibrosis progression.
Guide decisions on whether a liver biopsy is necessary.
Triage patients for specialist referral in primary care.
Evaluate treatment response in patients on antifibrotic therapy.
Combine with APRI score for a more complete fibrosis picture.

Frequently Asked Questions

Last updated: 2026-07-23 · Reviewed by Nham Vu