FIB-4 Index

Non-invasive score used to estimate liver fibrosis in chronic liver disease.

Gastroenterology GastroenterologyEvidence-BasedUpdated 2026-07

Clinical decision-support tool for qualified healthcare professionals. Results are not a diagnosis and should not replace professional clinical judgment.

Clinical Notes

The FIB-4 Index is widely used to estimate the risk of advanced liver fibrosis in chronic hepatitis and fatty liver disease.

Calculator Information

Specialty

Gastroenterology

📋 Reference Ranges

Reference ranges for this calculator
Classification	Range
Low Risk	<1.30
Intermediate Risk	1.30–2.67
High Risk	>2.67

What This Calculator Measures

Calculates the FIB-4 index, a non-invasive score using age, AST, ALT, and platelet count to estimate the probability of advanced liver fibrosis in chronic liver disease.

How to Use

Enter the patient's age, AST, ALT, and platelet count.
Use steady-state liver enzymes rather than values from an acute hepatitis flare.
Interpret the result against the 1.30 and 2.67 thresholds.
For indeterminate results, consider additional testing such as elastography before referral decisions.

How the Calculation Works

FIB-4 = (age x AST) / (platelets x sqrt(ALT)), with age in years, AST and ALT in U/L, and platelets in x10^9/L.

Variables Explained

Age

Age in years, multiplied by AST in the numerator.

AST

Aspartate aminotransferase in U/L, multiplied by age in the numerator.

ALT

Alanine aminotransferase in U/L, square-rooted in the denominator.

Platelet Count

Platelet count in x10^9/L, multiplied by the square root of ALT in the denominator.

Interpretation Guide

FIB-4 <1.30 indicates low probability of advanced fibrosis; 1.30–2.67 is indeterminate (intermediate risk); >2.67 indicates high probability of advanced fibrosis. Performance is reduced under age 35.

Age-specific interpretation

Clinical Significance

FIB-4 is a widely recommended first-line, inexpensive fibrosis risk tool that helps primary-care clinicians identify patients needing specialty evaluation without unnecessary liver biopsy.

When It Is Useful

Screening for advanced fibrosis in NAFLD/MASLD and viral hepatitis
Primary-care risk stratification before hepatology referral
Serial follow-up of fibrosis risk in chronic liver disease

When It Is Not Useful

Patients younger than 35 years, where the score underperforms
Acute hepatitis flares with rapidly changing transaminases
Children and adolescents
To replace elastography or biopsy when fibrosis staging is required

Common Mistakes

Applying FIB-4 to patients younger than 35 years, where the score underperforms and low or high results should be interpreted with particular caution.
Omitting the square root on ALT or swapping platelets with ALT in the formula, which yields a number that cannot be compared with the 1.30 and 2.67 cutoffs.
Entering an AST upper limit of normal out of habit from using APRI, since FIB-4 uses the raw AST and ALT values directly and has no ULN input.

Limitations

The indeterminate range (1.30–2.67) requires further evaluation and does not resolve the question alone.
Age heavily influences the score, limiting accuracy at extremes.
Thrombocytopenia from non-hepatic causes confounds the platelet component.

Worked Example

A 55-year-old man with metabolic dysfunction-associated steatohepatitis has AST 45 U/L, ALT 60 U/L, and platelets 200 ×10⁹/L.

Inputs:

age: 55

ast: 45

alt: 60

platelets: 200

Expected Result: FIB-4 = (55 × 45) / (200 × √60) ≈ 1.6 — indeterminate risk (1.30–2.67); further assessment with elastography is reasonable.

Evidence & References

Source:: Hepatology Literature
Content updated:: 2026-08

Sterling RK, et al. Hepatology. 2006;43:1317-1325.

References

Sterling RK, et al. Development of a simple noninvasive index to predict significant fibrosis in patients with HIV/HCV coinfection. Hepatology. 2006;43:1317-1325. (Original model)

Frequently Asked Questions

How is FIB-4 different from APRI?

FIB-4 combines age, AST, ALT, and platelet count, while APRI uses only AST relative to its upper limit of normal and the platelet count. Because FIB-4 includes age and ALT, it draws on more of the routine panel, but age also drives its accuracy and limits performance under 35 years. Both are non-invasive estimates, not fibrosis diagnoses.

What does an indeterminate FIB-4 of 1.30 to 2.67 mean?

It means the score cannot resolve advanced fibrosis on its own. Results below 1.30 indicate low probability and results above 2.67 indicate high probability, but the middle range requires further evaluation such as elastography or other confirmatory testing. Patients in this band should not be reassured or labeled as having advanced fibrosis based on the number alone.

Why does age matter so much in FIB-4?

Age appears in the numerator, so the score rises with age even when liver tests are unchanged. This helps capture fibrosis risk in older adults but limits accuracy at the extremes of age, which is why performance is reduced under 35 years. When following a patient over time, expect the score to drift upward as the patient ages.

Disclaimer: This calculator is intended for educational and clinical decision support purposes only. FIB-4 is a screening index and does not replace clinical evaluation or confirmatory fibrosis testing.