FIB-4 Calculator
Calculate the FIB-4 index from age, AST, ALT, and platelet count to assess liver fibrosis risk.
What Is the FIB-4 Index?
The FIB-4 index is a non-invasive score used to estimate liver fibrosis risk in patients with chronic liver disease, especially hepatitis C and non-alcoholic fatty liver disease (NAFLD). It combines age, aspartate aminotransferase (AST), alanine aminotransferase (ALT), and platelet count from routine blood work. For broader liver assessment, see the Maddrey Discriminant Function Calculator and Child-Pugh Calculator.
Formula
$$FIB\text{-}4 = \frac{\text{Age (years)} \times \text{AST (U/L)}}{\text{Platelets (} \times 10^9\text{/L)} \times \sqrt{\text{ALT (U/L)}}}$$
Interpretation
- Below 1.45: low probability of advanced fibrosis
- 1.45 to 3.25: indeterminate; consider elastography or specialist referral
- Above 3.25: advanced fibrosis or cirrhosis likely
FIB-4 is a screening tool, not a diagnosis. Clinical context, imaging, and sometimes liver biopsy remain essential for definitive staging.
Frequently Asked Questions
What is a normal FIB-4 score?
Scores below 1.45 generally indicate low risk of advanced fibrosis. Values between 1.45 and 3.25 are indeterminate, and scores above 3.25 suggest significant fibrosis may be present.
What lab units does FIB-4 use?
Age is in years, AST and ALT in U/L (IU/L), and platelets in ×10⁹/L (equivalent to 10³/µL). Using consistent units is critical for an accurate result.
Who should use the FIB-4 calculator?
FIB-4 is validated mainly for adults with chronic liver disease such as viral hepatitis or NAFLD. It is not intended for acute hepatitis, children, or transplant recipients without specialist guidance.
Why is age included in FIB-4?
Liver fibrosis risk increases with age. Including age improves the index's ability to distinguish low-risk from high-risk patients when combined with liver enzymes and platelets.
What if my FIB-4 is indeterminate?
Scores from 1.45 to 3.25 do not clearly rule in or out advanced fibrosis. Your clinician may order transient elastography (FibroScan), additional blood tests, or biopsy depending on your history.
Can FIB-4 replace a liver biopsy?
No. FIB-4 helps triage patients and reduce unnecessary biopsies, but biopsy or advanced imaging may still be required when results are borderline or when management decisions depend on precise staging.
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