How it's calculated
FIB-4 = (Age × AST [SGOT]) ÷ (Platelet count × √ALT [SGPT]). It combines age with three routine blood tests to estimate the probability of advanced liver fibrosis.
Interpretation
| FIB-4 | Interpretation |
|---|---|
| < 1.45 | Low probability of advanced fibrosis |
| 1.45 – 3.25 | Indeterminate |
| > 3.25 | High probability of advanced fibrosis |
Clinical use
- FIB-4 is widely used as a first-line, no-additional-cost fibrosis screen in NAFLD/MASLD and chronic hepatitis populations, using tests already commonly available from routine blood work.
- A low FIB-4 (<1.45) has a strong negative predictive value for advanced fibrosis, making it useful for ruling out significant liver disease in primary care without further specialist referral.
- An indeterminate or high FIB-4 typically prompts referral for further assessment (elastography, specialist hepatology review) rather than an immediate biopsy.
- FIB-4 accuracy is reduced at the extremes of age (paediatric and very elderly populations), where age-related increases in the score can overestimate fibrosis risk.
Frequently asked questions
What is the FIB-4 index used for?
It's a simple, noninvasive screen for advanced liver fibrosis, calculated from age, AST, ALT, and platelet count — commonly used as a first-line test in fatty liver disease and chronic hepatitis to decide who needs further specialist assessment.
Is FIB-4 more accurate than APRI?
Both are simple, validated noninvasive screens with broadly similar performance; some studies suggest FIB-4 performs slightly better in NAFLD/MASLD populations, but neither replaces elastography or biopsy for a precise fibrosis stage.
Can FIB-4 be used in older or younger patients?
Caution is needed at the extremes of age — FIB-4 incorporates age directly into the formula, so scores can be less reliable and tend to overestimate fibrosis risk in elderly patients, and the score isn't validated in children.
What should happen if my FIB-4 score is indeterminate or high?
This generally prompts referral for further assessment — such as transient elastography (FibroScan) or specialist hepatology review — rather than assuming advanced fibrosis is present or absent based on FIB-4 alone.
References
- Sterling RK, et al. Development of a simple noninvasive index to predict significant fibrosis in patients with HIV/HCV coinfection. Hepatology. 2006;43:1317-1325.
- European Association for the Study of the Liver (EASL). Clinical Practice Guidelines on Non-Invasive Tests for Evaluation of Liver Disease Severity and Prognosis.
- McPherson S, et al. Simple non-invasive fibrosis scoring systems can reliably exclude advanced fibrosis in patients with NAFLD. Gut. 2010;59:1265-1269.