FIB-4 Score (Liver Fibrosis)

The Fibrosis-4 Index (FIB-4) is a non-invasive, blood-based scoring tool used to estimate the degree of hepatic fibrosis in patients with chronic liver disease, most commonly chronic hepatitis B, hepatitis C, and non-alcoholic fatty liver disease (NAFLD/MASLD). Developed by Sterling and colleagues in 2006 using data from HIV/HCV co-infected patients enrolled in the APRICOT trial, it uses four routinely available variables: patient age, AST (aspartate aminotransferase), platelet count, and ALT (alanine aminotransferase). The resulting score correlates with liver biopsy-staged fibrosis and allows non-invasive categorisation of patients into those with no/minimal fibrosis (F0–F1), indeterminate fibrosis requiring further testing, and advanced fibrosis/cirrhosis (F3–F4). The principal clinical value of FIB-4 is its ability to identify patients who are unlikely to have advanced fibrosis and can therefore be spared from liver biopsy and more invasive investigations. A FIB-4 score below 1.30 has a negative predictive value of approximately 90% for excluding advanced fibrosis, while a score above 2.67 has a positive predictive value of approximately 80% for confirming advanced fibrosis. The indeterminate zone (1.30–2.67) often requires supplementary testing such as liver stiffness measurement by transient elastography (FibroScan). FIB-4 is endorsed by multiple international hepatology and gastroenterology societies and is increasingly used as a first-line population-level screening tool in primary care for early identification of advanced liver disease.

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1. 1Collect four routine laboratory and demographic values: patient age in years, serum AST (aspartate aminotransferase) in U/L, serum ALT (alanine aminotransferase) in U/L, and platelet count in 10^9/L (or ×10³/µL).
2. 2Calculate the square root of the ALT value (√ALT). This accounts for the non-linear relationship between ALT and fibrosis stage.
3. 3Multiply the platelet count (in 10^9/L) by the square root of ALT to form the denominator.
4. 4Multiply age by AST to form the numerator — age amplifies the contribution of AST because fibrosis accumulates over time.
5. 5Divide the numerator (Age × AST) by the denominator (Platelets × √ALT) to obtain the FIB-4 index.
6. 6Apply the threshold interpretation: FIB-4 <1.30 = F0–F1 (advanced fibrosis unlikely, ~90% NPV); FIB-4 1.30–2.67 = indeterminate (refer for elastography); FIB-4 >2.67 = F3–F4 (advanced fibrosis likely, ~80% PPV).
7. 7Note: age-adjusted cut-offs are recommended — for patients aged ≥65 years, the lower cut-off rises to 2.0 (to reduce false positives from age-related platelet decline and AST changes).

• !Using platelet count in units other than 10^9/L — if the count is reported in 10^3/µL, the numeric value is identical and no conversion is needed; but if reported in individual platelets/µL, divide by 10^6 first.
• !Applying standard cut-offs to elderly patients (≥65 years) without raising the lower threshold to 2.0, leading to false-positive identification of advanced fibrosis in normal ageing.
• !Using FIB-4 in patients with acute hepatitis (alcoholic, ischaemic, or viral) where transaminases are transiently very high — FIB-4 is validated for chronic liver disease only.
• !Treating FIB-4 as diagnostic rather than probabilistic — a score >2.67 does not diagnose cirrhosis; it identifies patients who need confirmatory investigation.
• !Ignoring non-hepatic causes of AST elevation (haemolysis, myositis) when interpreting a high FIB-4 score, potentially misclassifying patients.
• !Not repeating FIB-4 annually in patients with risk factors for progressive liver disease — a single normal FIB-4 does not exclude progression over time.