FIB-4 Calculator
Calculate the FIB-4 Index to assess liver fibrosis risk using age, AST, ALT, and platelet count.
Interpretation Guide
| FIB-4 Score | Risk Level | Interpretation |
|---|---|---|
| <1.30 | Low Risk | Excludes advanced fibrosis (F3-F4) with high NPV |
| 1.30-2.67 | Indeterminate | Further evaluation recommended (elastography, biopsy) |
| >2.67 | High Risk | Suggests advanced fibrosis (F3-F4), specialist referral needed |
FIB-4 Formula
FIB-4 = (Age × AST) / (Platelets × √ALT)
Where:
- Age is in years
- AST (Aspartate Aminotransferase) is in U/L
- ALT (Alanine Aminotransferase) is in U/L
- Platelet count is in ×10⁹/L (or ×10³/μL)
Clinical Information
What is the FIB-4 Index?
The FIB-4 (Fibrosis-4) Index is a validated non-invasive scoring system used to assess the degree of liver fibrosis in patients with chronic liver disease. It was originally developed for hepatitis C patients but is now widely used across various liver conditions including NAFLD, hepatitis B, and alcohol-related liver disease.
When to Use FIB-4
- Screening for advanced fibrosis in chronic liver disease
- Monitoring disease progression in hepatitis C, B, or NAFLD
- Risk stratification before initiating antiviral therapy
- Determining need for specialist referral or further testing
- Assessing response to treatment over time
Advantages
- Non-invasive and readily available from routine blood tests
- Well-validated across multiple liver disease etiologies
- Cost-effective screening tool
- High negative predictive value for excluding advanced fibrosis
- Can be calculated at point of care
Limitations
- Less accurate in patients <35 or >65 years of age
- May be affected by extrahepatic conditions (hemolysis, medications)
- Cannot distinguish between intermediate stages of fibrosis
- Should be combined with other markers for optimal accuracy
- Does not replace liver biopsy when definitive staging needed
Clinical Recommendations
FIB-4 <1.30:
- Low probability of advanced fibrosis
- Continue routine monitoring
- Repeat assessment annually or as clinically indicated
FIB-4 1.30-2.67:
- Indeterminate risk, requires further evaluation
- Consider vibration-controlled transient elastography (FibroScan)
- May need additional biomarkers (Enhanced Liver Fibrosis score)
- Consider hepatology referral based on clinical context
FIB-4 >2.67:
- High probability of advanced fibrosis (F3-F4)
- Refer to hepatology specialist
- Consider liver biopsy or elastography for staging
- Screen for complications (varices, hepatocellular carcinoma)
- Initiate appropriate treatment if not already started
Frequently Asked Questions
What does a high FIB-4 score mean?
A FIB-4 score greater than 2.67 suggests a high probability of advanced liver fibrosis (stages F3-F4). This indicates significant scarring of the liver and warrants specialist evaluation, further diagnostic testing, and appropriate management to prevent progression to cirrhosis.
How accurate is the FIB-4 calculator?
FIB-4 has been extensively validated with an AUROC (Area Under Receiver Operating Characteristic curve) of 0.765-0.85 for detecting advanced fibrosis. It has excellent negative predictive value (NPV) of approximately 90% for excluding advanced fibrosis when the score is below 1.30, but lower positive predictive value, which is why indeterminate scores require further testing.
Can FIB-4 be used for all types of liver disease?
While FIB-4 was originally developed for hepatitis C, it has been validated for various chronic liver diseases including NAFLD/NASH, hepatitis B, alcohol-related liver disease, and HIV/HCV co-infection. However, it should be interpreted cautiously in patients with acute liver injury, biliary obstruction, or hematologic disorders.
How often should FIB-4 be calculated?
For patients with chronic liver disease, FIB-4 should be calculated annually or when there are significant clinical changes. In patients on treatment for viral hepatitis or NAFLD, more frequent monitoring (every 6-12 months) may be appropriate to assess treatment response and disease progression.
What should I do if my FIB-4 score is indeterminate?
An indeterminate FIB-4 score (1.30-2.67) indicates that the test cannot reliably exclude or confirm advanced fibrosis. In this case, additional testing is recommended, such as transient elastography (FibroScan), Enhanced Liver Fibrosis (ELF) test, or consideration of liver biopsy. Consult with a hepatologist to determine the most appropriate next steps.
Does age affect FIB-4 score?
Yes, age is a component of the FIB-4 formula, and the score naturally increases with age. This can lead to overestimation of fibrosis in elderly patients (>65 years) and underestimation in young patients (<35 years). Alternative cutoffs or additional testing may be needed in these age groups for accurate assessment.
Can FIB-4 replace liver biopsy?
FIB-4 is a useful screening tool and can help avoid unnecessary biopsies in low-risk patients, but it cannot completely replace liver biopsy. Biopsy remains the gold standard for definitive staging of fibrosis, assessing inflammatory activity, and diagnosing certain liver conditions. FIB-4 is best used as part of a comprehensive assessment strategy.
What factors can affect FIB-4 accuracy?
Several factors can impact FIB-4 accuracy including extreme age (<35 or >65), hemolysis (elevates AST), Gilbert's syndrome, muscle disorders, medications affecting liver enzymes, thrombocytopenia from non-hepatic causes, and acute liver injury. Clinical correlation and consideration of these factors is essential for proper interpretation.
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