Fibrosis-4 (FIB-4) Index

Understanding the FIB-4 Index

The Fibrosis-4 (FIB-4) Index is a non-invasive scoring system used to assess the severity of liver fibrosis. It was initially developed for patients with HIV/HCV coinfection but has since been validated for various liver conditions. The index combines age, AST, ALT, and platelet count to estimate the amount of scarring in the liver.

What is the FIB-4 Index?

The FIB-4 Index is calculated using the following formula:

• FIB-4 = (Age × AST) / (Platelets × √ALT)

Interpretation of Results

FIB-4 Score Ranges

• < 1.45: Low probability of advanced fibrosis (negative predictive value 90%)
• 1.45 - 3.25: Indeterminate range, biopsy may be needed
• > 3.25: High probability of advanced fibrosis (specificity 97%, positive predictive value 65%)

Using these cutoff values:

• About 70% of patients will fall outside the indeterminate range
• Overall accuracy is approximately 87% for those outside the indeterminate range
• Only about 30% of patients will need a liver biopsy for definitive staging

The FIB-4 Index was initially validated in patients with HIV/HCV coinfection but has since been validated for various liver conditions.

Clinical Significance

The FIB-4 Index is valuable for:

• Initial screening for liver fibrosis
• Monitoring disease progression
• Reducing the need for liver biopsy
• Risk stratification in liver disease

Important Considerations

• Results should be interpreted by a healthcare professional
• The index should be used alongside other clinical findings
• Regular monitoring may be necessary for chronic conditions
• Not all patients will fall clearly into one category

When to Use FIB-4 Index

Consider calculating FIB-4 in patients with:

• Chronic viral hepatitis
• Non-alcoholic fatty liver disease (NAFLD)
• Alcoholic liver disease
• Other chronic liver conditions

Limitations

This calculator:

• Provides estimates based on input values
• Should not replace clinical judgment
• May not be accurate in all patient populations
• Has an indeterminate range requiring additional testing

Tips for Accurate Results

1. Use recent laboratory values
2. Ensure correct units are selected
3. Consider repeat testing if results are borderline
4. Account for factors that might affect individual components

Factors Affecting FIB-4 Components

AST and ALT levels can be affected by

• Medication use
• Recent alcohol consumption
• Exercise
• Other liver conditions

Platelet count can be affected by

• Bone marrow disorders
• Immune conditions
• Medications
• Recent infections

Clinical Applications

The FIB-4 Index is particularly useful for:

• Initial assessment of liver fibrosis
• Monitoring disease progression
• Determining need for additional testing
• Risk stratification
• Treatment planning

Start calculating now to better understand your liver health!

References:

1. Sterling RK, Lissen E, Clumeck N, et al. Development of a simple noninvasive index to predict significant fibrosis in patients with HIV/HCV coinfection. Hepatology. 2006;43(6):1317-1325.