Non-invasive screen for advanced liver fibrosis.
Source: Sterling et al., Hepatology 2006.
What does the FIB-4 score mean?
The FIB-4 (Fibrosis-4) score is a non-invasive index that estimates the degree of liver fibrosis (scarring) using four routine blood test values: age, AST (aspartate aminotransferase), ALT (alanine aminotransferase), and platelet count. It was originally developed by Sterling and colleagues (2006) in patients with HIV-hepatitis C co-infection and subsequently validated in NAFLD and other liver diseases.
The formula is: FIB-4 = (Age × AST) / (Platelets × √ALT). The logic is physiological: as liver fibrosis advances, the liver produces fewer clotting factors and platelet counts fall; AST rises as liver cells are damaged; ALT can plateau or fall in advanced disease. Age amplifies the relationship because fibrosis accumulates over time.
FIB-4 has been endorsed by several international guidelines, including the American Association for the Study of Liver Diseases (AASLD) and the European Association for the Study of the Liver (EASL), as a first-line non-invasive marker in NAFLD/MASLD screening pathways. A FIB-4 below 1.30 can confidently reassure that advanced fibrosis is unlikely (negative predictive value >90%); above 2.67, advanced fibrosis is probable (positive predictive value ~80%).
Important limitations: the test was validated primarily in adults aged 35–65 and in specific disease populations. In older adults (over 65), the sensitivity decreases because age itself raises the score. Active exercise can transiently raise AST and therefore FIB-4.
Reference ranges
| FIB-4 Score | Interpretation | Suggested action |
|---|---|---|
| < 1.30 | Low risk — advanced fibrosis unlikely | Reassurance; recheck in 1–2 years if risk factors persist |
| 1.30 – 2.67 | Indeterminate | Consider FibroScan or other fibrosis marker |
| > 2.67 | High risk — probable advanced fibrosis | Hepatology referral recommended |
When should you see a doctor?
Anyone with a FIB-4 above 1.30 and known liver disease risk factors (obesity, metabolic syndrome, diabetes, excess alcohol intake, or chronic hepatitis) should discuss the result with their doctor. A high FIB-4 does not diagnose liver disease, it signals that further investigation is warranted. Liver biopsy, FibroScan, or MR elastography can provide a more definitive fibrosis assessment.