FIB-4 Score Calculator
Calculate the FIB-4 (Fibrosis-4) index to estimate liver fibrosis risk using age, AST, ALT, and platelet count. A non-invasive screening tool used in hepatology. Educational reference only.
Formula & Reference
| Variable | Symbol | Formula | Units |
|---|---|---|---|
| FIB-4 Score Calculator | — | FIB-4 = (Age × AST) / (Platelets × √ALT) | index value |
Step-by-Step Examples
Age=35, AST=25, ALT=22, Platelets=250.
- FIB-4 = (35×25)/(250×√22) = 875/(250×4.69) = 875/1172.5 = 0.75
- Below the 1.3 threshold — low fibrosis risk
Age=55, AST=50, ALT=45, Platelets=180.
- FIB-4 = (55×50)/(180×√45) = 2750/(180×6.71) = 2750/1207.6 = 2.28
- Falls in the indeterminate range — may warrant additional evaluation
Age=65, AST=80, ALT=55, Platelets=120.
- FIB-4 = (65×80)/(120×√55) = 5200/(120×7.42) = 5200/890 = 5.84
- Well above 2.67 threshold — suggests high risk of advanced fibrosis
Real-World Applications
Common Mistakes to Avoid
FIB-4 is a screening risk stratification tool, not a diagnostic test. Indeterminate or high-risk results typically warrant further evaluation (imaging, specialist referral, sometimes biopsy).
Some research suggests age-specific cutoffs may improve accuracy, particularly distinguishing younger vs older patients, though the standard cutoffs remain widely used.
FIB-4 was originally developed and validated primarily for hepatitis C and HIV-coinfected patients, though it's now used more broadly across liver disease etiologies with reasonable performance.