What is the Fibrosis-4 (FIB-4) test and its interpretation?

From the Guidelines

The FIB-4 index is a valuable tool for assessing liver fibrosis, and a score below 1.3 can be used to rule out advanced fibrosis with a high negative predictive value, while a score above 3.25 suggests advanced fibrosis with a positive predictive value of approximately 65%. The FIB-4 index combines four readily available parameters: age, AST (aspartate aminotransferase), ALT (alanine aminotransferase), and platelet count, and is calculated using the formula: FIB-4 = (Age [years] × AST [U/L]) / (Platelets [10^9/L] × √ALT [U/L]) 1.

• The FIB-4 index is recommended as a first-line assessment for practitioners due to its simplicity and low cost 1.
• A score below 1.3 can be used to rule out advanced fibrosis with a high negative predictive value, allowing clinicians to exclude advanced fibrosis in patients with a low risk of liver-related outcomes 1.
• A score above 3.25 suggests advanced fibrosis (F3-F4) with a positive predictive value of approximately 65%, indicating a higher risk of liver-related outcomes 1.
• Scores between 1.3 and 3.25 fall in an indeterminate range, where additional testing like FibroScan or liver biopsy may be needed for accurate staging 1.
• The FIB-4 index has been validated in various liver diseases, including non-alcoholic fatty liver disease (NAFLD), and has good accuracy in predicting liver-related outcomes 1.
• However, the FIB-4 index should be interpreted in the clinical context, as factors like acute hepatitis, medication use, or other conditions affecting platelets or liver enzymes can influence results 1.

From the Research

FIB-4 Test Overview

• The FIB-4 index is a non-invasive tool used to predict liver fibrosis stage and clinical prognosis in patients with chronic liver disease 2.
• It is calculated based on age, aspartate aminotransferase (AST), and alanine aminotransferase (ALT) levels, and platelets count 3.

Interpretation of FIB-4 Results

• A FIB-4 index of less than 1.3 is generally considered low risk for advanced fibrosis, while a score of 3.25 or higher is considered high risk 4.
• The optimal cut-off values for FIB-4 may vary depending on the specific patient population and liver disease etiology 2, 5.
• For example, in patients with non-alcoholic fatty liver disease (NAFLD), a FIB-4 score of less than 1.45 may be used to exclude advanced fibrosis, while a score of 3.25 or higher may be used to predict advanced fibrosis 3.

Diagnostic Accuracy of FIB-4

• The FIB-4 index has been shown to have a relatively high diagnostic accuracy in predicting advanced fibrosis in patients with NAFLD, with an area under the receiver operating characteristic curve (AUC) value of 76% 6.
• The sensitivity and specificity of FIB-4 in detecting advanced fibrosis have been reported to be around 69% and 64%, respectively 6.
• FIB-4 may be used in combination with other non-invasive scoring systems, such as the NAFLD fibrosis score (NFS), to improve diagnostic accuracy 6.

Clinical Applications of FIB-4

• The FIB-4 index may be used as a screening tool in primary care settings to identify patients at high risk of advanced liver fibrosis 4.
• It may also be used to monitor disease progression and response to treatment in patients with chronic liver disease 2.
• FIB-4 has been shown to be associated with an increased risk of hepatocellular carcinoma and mortality in patients with viral hepatitis, NAFLD, and alcoholic liver disease 2.