Hepatology
FIB-4 (Fibrosis-4) Index
The FIB-4 index is a validated non-invasive fibrosis score for chronic hepatitis B/C and MASLD (NAFLD). Provide the patient’s age, transaminases, and platelet count to calculate the risk of advanced fibrosis.
Inputs
- Age: 52
- AST: 75
- ALT: 60
- Platelets: 180
FIB-4 score
2.80
Age-adjusted low cut-off (≥65 years: 2.0)
FIB-4 ≥ 2.67 suggests significant hepatic fibrosis. Refer for elastography, hepatology evaluation, or liver biopsy as indicated.
Combine with APRI, NAFLD Fibrosis Score, or elastography for comprehensive fibrosis assessment.
How to Use This Calculator
Obtain AST, ALT, platelet count, and age
Ensure labs are from the same visit and account for acute illnesses that might transiently elevate enzymes.
Enter values and review score
The calculator instantly updates the FIB-4 index and highlights risk band thresholds, including the higher low cut-off for patients >65 years.
Plan next steps
Low scores reassure; intermediate/high scores warrant elastography, hepatology referral, or biopsy depending on clinical context.
Formula
FIB-4 = (Age × AST) ÷ [Platelet count (×10⁹/L) × √ALT]
- Use the most recent laboratory results; AST and ALT in IU/L, platelets in ×10⁹/L.
- For patients older than 65 years, a higher low cut-off of 2.0 improves specificity.
- Common interpretation: <1.3 (low risk), 1.3–2.67 (indeterminate), ≥2.67 (high risk of advanced fibrosis).
Full Description
The Fibrosis-4 (FIB-4) index is a widely used non-invasive marker for liver fibrosis that combines age, AST, ALT, and platelet count. It was initially validated in hepatitis C and HIV/HCV co-infection, and later adopted for MASLD (NAFLD) triage in primary care.
FIB-4’s strength lies in its simplicity, but it can be confounded by acute hepatitis, thrombocytopenia of non-hepatic origin, or age extremes. Integrate the score with clinical judgment, imaging, and metabolic risk assessment before making therapeutic decisions.
Frequently Asked Questions
Can I use FIB-4 during acute hepatitis?
Scores may be falsely elevated. Reassess after resolution of acute inflammation to avoid overestimating fibrosis.
What if platelet count is low from other causes?
Thrombocytopenia due to hematologic or autoimmune issues may inflate FIB-4. Interpret with clinical context and alternative tests.
How does FIB-4 compare with NAFLD Fibrosis Score?
Both are recommended for MASLD triage. Using them together improves accuracy before sending patients for elastography.
Do I need to fast for AST/ALT labs?
Fasting is not mandatory, but avoid heavy exercise and alcohol before testing to reduce transient enzyme elevations.