What is the Fibrosis-4 (FIB-4) index?

From the Guidelines

The Fibrosis-4 (FIB-4) index is a noninvasive scoring system used to assess liver fibrosis, calculated using a simple algorithm based on age, alanine aminotransferase (ALT), aspartate aminotransferase (AST), and platelet count 1.

Key Components of FIB-4 Index

• Age: in years
• AST: aspartate aminotransferase in U/L
• ALT: alanine aminotransferase in U/L
• Platelet count: in 10^9/L The FIB-4 index is calculated as: FIB-4 = age x AST / (platelet count x √ALT) 1.

Interpretation of FIB-4 Index

• FIB-4 < 1.3: low risk of advanced fibrosis, with a negative predictive value of ≥90% 1
• FIB-4 > 2.67: high risk of advanced fibrosis, with a positive predictive value of 60-80% 1
• FIB-4 between 1.3 and 2.67: indeterminate range, requiring further evaluation 1 It is essential to consider patient age when interpreting FIB-4 values, as the diagnostic value of FIB-4 decreases in patients under 35 years old, and an age-adjusted lower cutoff value of 2.0 is recommended for elderly patients aged ≥65 years old 1.

From the Research

Definition of FIB-4 Index

• The FIB-4 index is a non-invasive tool used to assess liver fibrosis, calculated based on age, aspartate aminotransferase (AST), and alanine aminotransferase (ALT) levels, and platelets count 2, 3, 4.
• It is used to identify patients with advanced fibrosis and cirrhosis, and to predict the risk of severe liver outcomes, such as hepatocellular carcinoma and liver transplantation 3, 5.

Calculation and Interpretation of FIB-4 Index

• The FIB-4 index is calculated using a formula that combines the above-mentioned parameters 4.
• The results of the FIB-4 index are interpreted as follows:
  • Low risk: FIB-4 index < 1.45, indicating a low risk of advanced fibrosis 4, 6.
  • Indeterminate risk: FIB-4 index between 1.45 and 3.25, indicating an uncertain risk of advanced fibrosis 4, 6.
  • High risk: FIB-4 index ≥ 3.25, indicating a high risk of advanced fibrosis and cirrhosis 4, 6.

Clinical Applications of FIB-4 Index

• The FIB-4 index can be used as a screening tool in primary care settings to identify patients at high risk of liver fibrosis and cirrhosis 2, 5, 6.
• It can also be used to monitor patients with chronic liver disease and to predict the risk of severe liver outcomes 3, 5.
• The FIB-4 index has been shown to be accurate in predicting the absence or presence of advanced fibrosis in patients with non-alcoholic fatty liver disease (NAFLD) and viral hepatitis 3, 4.