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FIB-4 Index

Non-invasive liver fibrosis assessment using routine lab values

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Why use it

Non-invasive, inexpensive fibrosis assessment using routine labs. Recommended as first-line screening for advanced fibrosis in NAFLD (AASLD/EASL guidelines). Reduces unnecessary liver biopsies and specialist referrals.

About

The FIB-4 Index is a non-invasive marker for hepatic fibrosis using readily available laboratory values: age, AST, ALT, and platelet count. Originally validated in HIV/HCV co-infection, it is now widely used for NAFLD/NASH, hepatitis B, and other chronic liver diseases. It helps determine which patients need further evaluation (e.g., FibroScan or liver biopsy).

When to use

  • Screening for advanced fibrosis in NAFLD/NASH
  • Chronic hepatitis B or C fibrosis assessment
  • Primary care screening before hepatology referral
  • Longitudinal monitoring of fibrosis progression

Formula

FIB-4 = (Age × AST) / (Platelets × √ALT) Age in years, AST and ALT in U/L, Platelets in 10⁹/L

Pearls & pitfalls

  • FIB-4 < 1.30 has > 90% negative predictive value for excluding advanced fibrosis.
  • Less reliable in patients < 35 or > 65 years (age is a component of the formula).
  • For patients > 65, a higher cutoff of < 2.0 for low risk may be more appropriate.
  • Platelet count can be falsely low due to non-hepatic causes (ITP, medications).
  • Acute hepatitis with very high AST/ALT can falsely elevate FIB-4.
  • Combine with FibroScan for best non-invasive fibrosis staging.

Next steps

FIB-4 < 1.30: Low risk for advanced fibrosis, reassess in 1-2 years. FIB-4 1.30-2.67: Indeterminate — proceed to FibroScan or ELF test. FIB-4 > 2.67: High probability of advanced fibrosis — refer to hepatology.

Evidence

Developed by Sterling et al. (Hepatology 2006) in HIV/HCV patients. Extensively validated in NAFLD populations. Endorsed by AASLD (2023), EASL (2021), and AGA (2020) guidelines for NAFLD fibrosis screening.

References

  1. Sterling RK et al. Development of a simple noninvasive index to predict significant fibrosis in patients with HIV/HCV coinfection. Hepatology. 2006;43(6):1317-1325. — link
  2. Shah AG et al. Comparison of noninvasive markers of fibrosis in patients with nonalcoholic fatty liver disease. Clin Gastroenterol Hepatol. 2009;7(10):1104-1112. — link