How is the Aspartate Aminotransferase (AST) to Platelet Ratio Index (APRI) score calculated in Hepatitis B?

APRI Score Calculation in Hepatitis B

The APRI (AST to Platelet Ratio Index) score in hepatitis B is calculated using the formula: (AST/upper limit of normal for AST) × 100/platelet count (×10^9/L). 1

Formula Breakdown

• The formula consists of two main components:
  • AST value divided by the upper limit of normal (ULN) for AST 1
  • Platelet count in 10^9/L (standard units for platelets) 1
  • The formula is: (AST/ULN for AST) × 100/platelet count 1

Clinical Significance and Cutoff Values

For Significant Fibrosis (≥F2)

• Low cutoff: APRI >0.5

  • Sensitivity: 72.9% (95% CI: 70.2-75.5%)
  • Specificity: 64.7% (95% CI: 61.0-68.2%) 1
  • This cutoff identifies most patients with significant fibrosis while minimizing false negatives 1

• High cutoff: APRI >1.5

  • Sensitivity: 30.5% (95% CI: 23.7-38.3%)
  • Specificity: 92.3% (95% CI: 89.3-94.6%) 1
  • More specific but less sensitive for significant fibrosis 1

For Cirrhosis (F4)

• Low cutoff: APRI >1.0

  • Sensitivity: 59.4% (95% CI: 53.2-65.2%)
  • Specificity: 73.9% (95% CI: 70.1-77.4%) 1
  • Recommended by WHO guidelines to identify most adults with cirrhosis 1

• High cutoff: APRI >2.0

  • Sensitivity: 30.2% (95% CI: 24.2-36.9%)
  • Specificity: 88.2% (95% CI: 85.4-90.6%) 1
  • Higher specificity but lower sensitivity for cirrhosis 1

Practical Application

• APRI is recommended as a preferred non-invasive test due to:

  • Low cost (requires only AST and platelet count) 1
  • Wide availability of required tests in most healthcare facilities 1
  • Can be performed by untrained personnel 1
  • Straightforward interpretation 1

• In a population with 25% prevalence of significant fibrosis:

  • Using APRI >0.5 would result in 26.2% false positives but only 6.8% false negatives 1
  • This approach prioritizes identifying patients who need treatment 1

Limitations and Considerations

• APRI has moderate diagnostic accuracy with AUROCs of:

  • 0.79 for significant fibrosis in HBV patients 2
  • 0.75 for cirrhosis in HBV patients 2

• Dual cutoffs (low to rule out, high to rule in) improve diagnostic accuracy but result in indeterminate results for patients falling between cutoffs 1

• APRI performance may be influenced by:

  • Acute hepatitis with severe inflammation 1
  • Conditions affecting AST levels or platelet counts 1
  • Hemolysis or Gilbert syndrome (can affect test components) 1

Comparison with Other Non-invasive Tests

• APRI is simpler but slightly less accurate than FibroScan:

  • For significant fibrosis (≥F2): APRI AUROC 0.79 vs. FibroScan AUROC 0.83 3
  • For cirrhosis (F4): APRI AUROC 0.75 vs. FibroScan AUROC 0.89 1, 3

• FIB-4 may have slightly better performance than APRI for advanced fibrosis and cirrhosis in HBV patients 3

• WHO guidelines recommend either APRI >0.5 or FibroScan >7.0 kPa to identify significant fibrosis, and either APRI >1.0 or FibroScan >12.5 kPa to identify cirrhosis 1