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Hepatobiliary
Demonstration data

FIB-4 Index

Non-invasive index estimating hepatic fibrosis from age, transaminases and platelet count.

The FIB-4 index combines age, AST, ALT and platelet count into a simple non-invasive marker of hepatic fibrosis. It is widely used to triage patients with chronic liver disease (including NAFLD and viral hepatitis) toward or away from further fibrosis assessment.

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📐 Formula

FIB-4 = (age × AST) / (platelets × √ALT)

When to Use

  • Initial non-invasive fibrosis staging in chronic liver disease.
  • Ruling out advanced fibrosis to avoid unnecessary elastography or biopsy.
  • Population-level triage of NAFLD/MASLD.

How It Works

  • Collect patient age, AST, ALT (U/L) and platelet count (×10⁹/L).
  • FIB-4 = (age × AST) / (platelets × √ALT).
  • Apply the low and high thresholds to classify fibrosis risk.

Interpreting the Result

  • FIB-4 < 1.45: low probability — advanced fibrosis effectively excluded (high negative predictive value).
  • FIB-4 1.45–3.25: indeterminate — consider elastography or further assessment.
  • FIB-4 > 3.25: high probability of advanced fibrosis (F3–F4).

Limitations & Pitfalls

  • The 1.45 cut-off performs less well in patients over 65; an age-adjusted threshold (~2.0) is often used.
  • Acute hepatitis, other causes of thrombocytopenia and extreme transaminase elevations reduce accuracy.
  • It stages fibrosis probabilistically and does not replace elastography or biopsy when definitive staging is required.

References

  • Sterling RK, Lissen E, Clumeck N, et al. Development of a simple noninvasive index to predict significant fibrosis in patients with HIV/HCV coinfection. Hepatology. 2006;43(6):1317-1325.
  • Shah AG, Lydecker A, Murray K, et al. Comparison of noninvasive markers of fibrosis in patients with nonalcoholic fatty liver disease. Clin Gastroenterol Hepatol. 2009;7(10):1104-1112.

⚕️ For clinical decision support only. Always verify calculations and apply clinical judgment.