FIB-4 Index

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

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

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.

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 to Use

• 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 Not to Use

• 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

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.

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

Evidence

Source

Hepatology Literature

Reference

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.

Reviewed By

MedCalcHub Clinical Team

Version

1.0

Updated

2026-08

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

References

1. 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)