From the Guidelines
To calculate the FIB-4 score for liver fibrosis using SI units, use the formula: FIB-4 = (Age × AST) / (Platelets × √ALT). Age is in years, AST (aspartate aminotransferase) and ALT (alanine aminotransferase) are in U/L, and platelets are in 10^9/L. For example, if a patient is 50 years old with AST of 60 U/L, ALT of 40 U/L, and platelets of 150 × 10^9/L, the calculation would be: (50 × 60) / (150 × √40) = 3000 / (150 × 6.32) = 3000 / 948 = 3.16.
Key Points to Consider:
- A FIB-4 score below 1.3 suggests minimal fibrosis, while a score above 2.67 indicates advanced fibrosis or cirrhosis 1.
- Values between 1.3 and 2.67 are indeterminate and may require additional testing.
- The FIB-4 score works by combining markers of liver inflammation (AST and ALT) with age and platelet count, which tends to decrease as fibrosis progresses due to portal hypertension and splenic sequestration.
- This non-invasive test helps clinicians assess liver fibrosis severity without requiring a liver biopsy.
- The FIB-4 score is recommended as a first-line assessment for practitioners based on its simplicity and low cost 1.
- Patients with FIB-4 score >2.67 are at high risk for advanced fibrosis, with most studies reporting positive predictive values of 60%–80% 1.
- The use of TE and/or patented serum tests should be used to rule-out/in advanced fibrosis in patients with FIB-4 over 1.3 1.
From the Research
Calculating FIB-4 Score
To calculate the FIB-4 score for liver fibrosis using SI units, the following formula can be used:
- FIB-4 score = (age * AST) / (platelet count * ALT^0.5) 2 Where:
- Age is in years
- AST is aspartate aminotransferase in U/L
- Platelet count is in 10^9/L
- ALT is alanine aminotransferase in U/L
Components of FIB-4 Score
The FIB-4 score is based on the following components:
- Age: older age is associated with higher FIB-4 scores 2
- AST: elevated AST levels are associated with higher FIB-4 scores 2
- Platelet count: lower platelet counts are associated with higher FIB-4 scores 2, 3
- ALT: elevated ALT levels are associated with lower FIB-4 scores 2
Comparison with Other Scores
The FIB-4 score has been compared with other scores, such as the APRI score, and has been shown to have similar diagnostic accuracy for liver fibrosis 2, 3, 4