FIB-4 Index for Liver Fibrosis

The FIB-4, or Fibrosis-4 Index, is a widely used non-invasive score to estimate the risk of advanced liver fibrosis and cirrhosis, primarily in patients with chronic liver diseases such as hepatitis C (HCV) and non-alcoholic fatty liver disease (NAFLD). It was developed as a simple, low-cost alternative to liver biopsy, which is an invasive procedure. The FIB-4 calculation is based on four routinely available variables: the patient's age (in years), serum levels of aspartate aminotransferase (AST) and alanine aminotransferase (ALT), and the platelet count. The exact formula is [Age x AST] / (Platelets x square root of ALT). The interpretation of the result depends on established cutoff points: a low value (e.g., often < 1.45) has a high negative predictive value, making advanced fibrosis unlikely and potentially avoiding further procedures. Conversely, a high value (e.g., > 3.25) suggests a high probability of advanced fibrosis or cirrhosis, indicating the need for more in-depth assessment and management. Values that fall into the 'indeterminate' zone, between the lower and upper cutoffs, are inconclusive and usually require further investigation, such as other non-invasive markers or, in some cases, a liver biopsy. Therefore, FIB-4 is a screening and risk stratification tool, not a definitive diagnosis in itself.