AST to Platelet Ratio Index (APRI)
Understanding APRI
The AST to Platelet Ratio Index (APRI) is a simple, non-invasive tool used to assess liver fibrosis and cirrhosis, particularly in patients with chronic hepatitis C. It uses routine laboratory results - AST (Aspartate Aminotransferase) and platelet count - to help predict liver disease severity.
What is APRI?
APRI is calculated using the formula:
- APRI = [(AST / AST Upper Limit of Normal) / Platelet Count] × 100
The result helps healthcare providers assess the likelihood of significant liver fibrosis or cirrhosis without requiring a liver biopsy.
Interpreting APRI Results
For Significant Fibrosis:
- APRI < 0.5: Helps rule out significant fibrosis (high negative predictive value)
- APRI > 0.7: Suggests significant fibrosis (sensitivity 77%, specificity 72%)
- APRI > 1.5: Helps rule in significant fibrosis (high positive predictive value)
For Cirrhosis:
- APRI < 0.5: Helps rule out cirrhosis (high negative predictive value)
- APRI > 1.0: Suggests cirrhosis (sensitivity 76%, specificity 72%)
- APRI > 2.0: High specificity for cirrhosis (specificity 91%, sensitivity 46%)
Values between these cutoffs fall in an indeterminate range and may require additional testing.
Clinical Significance
APRI is useful for:
- Initial screening for liver fibrosis
- Monitoring disease progression
- Assessing need for further testing
- Treatment decision-making
Important Considerations
- Results should be interpreted by a healthcare professional
- APRI is most validated in hepatitis C patients
- Other causes of elevated AST or low platelets can affect results
- Consider combining with other non-invasive tests (e.g., FibroTest) for better accuracy
- Midrange values are less diagnostically helpful
When to Use APRI
APRI is particularly useful when:
- Evaluating chronic liver disease
- Screening for significant fibrosis
- Monitoring disease progression
- Assessing treatment response
- Liver biopsy is not feasible
Limitations
This calculator:
- Is not diagnostic on its own
- May have reduced accuracy in certain conditions
- Should be used alongside clinical judgment
- May need confirmation with other tests
Tips for Accurate Results
- Use recent laboratory values
- Ensure correct units are selected
- Consider repeat testing if results are borderline
- Use alongside other clinical findings
Factors Affecting APRI
AST levels can be affected by
- Liver disease
- Muscle damage
- Medications
- Recent exercise
- Other medical conditions
Platelet count can be affected by
- Liver disease
- Bone marrow conditions
- Medications
- Bleeding disorders
- Infections
Clinical Applications
APRI is particularly valuable in:
- Resource-limited settings
- Initial screening
- Monitoring known liver disease
- Research studies
- Treatment decision-making
Start calculating now to assess liver fibrosis risk!
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