FIB-4 Index Calculator
Calculate the Fibrosis-4 index for non-invasive liver fibrosis assessment.
What is the FIB-4 Index?
The FIB-4 index is a non-invasive tool used by clinicians to estimate the amount of scarring (fibrosis) in the liver. It was originally developed to assess liver disease in patients with HIV and Hepatitis C co-infections, but it is now widely used for Non-Alcoholic Fatty Liver Disease (NAFLD) and other chronic liver conditions.
How the FIB-4 Score is Calculated
The calculation uses four specific parameters that are typically part of routine blood work:
- Age: Patients with higher age naturally have a different risk profile.
- AST (Aspartate Aminotransferase): A liver enzyme that increases with liver damage.
- ALT (Alanine Aminotransferase): Another liver enzyme; the ratio of AST to ALT is significant.
- Platelet Count: As liver disease progresses to cirrhosis, platelet counts typically drop due to splenic sequestration.
The Formula:
FIB-4 = (Age × AST) / (Platelet Count × √ALT)
Interpreting the Results
The FIB-4 index is primarily used to rule out advanced fibrosis. The general clinical cut-off values for adults are:
| Score | Interpretation | Action |
|---|---|---|
| < 1.45 | Low Risk | Advanced fibrosis is unlikely. High negative predictive value. |
| 1.45 – 3.25 | Intermediate Risk | Indeterminate. Further testing (like FibroScan) may be needed. |
| > 3.25 | High Risk | Advanced fibrosis or cirrhosis is likely. Referral to specialist recommended. |
Example Calculation
Suppose a 50-year-old patient has an AST of 40 U/L, an ALT of 35 U/L, and a platelet count of 200 (10³/µL).
1. Age (50) × AST (40) = 2,000
2. √ALT (√35) ≈ 5.916
3. Platelets (200) × 5.916 = 1,183.2
4. 2,000 / 1,183.2 = 1.69
This patient falls into the "Intermediate Risk" category, suggesting the need for monitoring or additional diagnostics.
Disclaimer: This calculator is for educational purposes only. It should not be used as a substitute for professional medical advice, diagnosis, or treatment. Always consult with a healthcare provider regarding liver health.