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Fibrosis-4 (FIB-4) Index for Liver Fibrosis

Non-invasive estimate of advanced liver fibrosis from age and routine labs.

Fibrosis-4 (FIB-4) Index for Liver Fibrosis
Age
years
AST
U/L
ALT
U/L
Platelet count
x10^9/L
Complete the fields above to see the result.

When to use

  • First-line non-invasive triage for advanced fibrosis in chronic hepatitis C/B and NAFLD/MASLD before referral for elastography or biopsy.

Formula

FIB-4 = (Age[years] x AST[U/L]) / (Platelets[x10^9/L] x sqrt(ALT[U/L])). <1.45 = low probability of advanced fibrosis; >3.25 = high probability; 1.45-3.25 = indeterminate.

Pearls and pitfalls

  • Originally derived and validated in HIV/HCV co-infected patients; widely used since in NAFLD/MASLD.
  • Age-dependent — less accurate at the extremes of age, particularly in patients under 35 or over 65 years.

References

  1. Sterling RK, et al. Development of a simple noninvasive index to predict significant fibrosis in patients with HIV/HCV co-infection. Hepatology. 2006;43(6):1317-25.