APRI (AST to Platelet Ratio Index) Calculator
The AST-to-Platelet Ratio Index (APRI) is a non-invasive estimate of liver fibrosis: (AST ÷ AST upper limit of normal × 100) ÷ platelet count. Lower values make significant fibrosis unlikely; higher values make it likely.
Quick answer
The AST-to-Platelet Ratio Index (APRI) is a non-invasive estimate of liver fibrosis: APRI = (AST ÷ AST upper limit of normal × 100) ÷ platelet count (×10⁹/L). An APRI of 0.5 or less makes significant fibrosis unlikely, while values above 1.0–1.5 increasingly suggest significant fibrosis or cirrhosis in chronic hepatitis C.
APRI inputs
Validated formula
APRI = ( (AST / AST upper-limit-of-normal) × 100 ) / platelet count (×10⁹/L). AST ULN is the lab reference (40 IU/L in the original study).
Interpretation
- ≤0.5— Significant fibrosis unlikely (rules out significant fibrosis with high NPV).
- >0.7— Significant fibrosis (≥F2) likely — sensitivity 77%, specificity 72%.
- >1.0— Cirrhosis suggested in chronic hepatitis C — sensitivity 76%, specificity 72% for cirrhosis.
- ≥1.5— Rules in significant fibrosis with high specificity.
How to use the APRI calculator
- 1Enter AST and its upper limit. Enter the AST result and the laboratory upper limit of normal for AST (commonly 40 IU/L in the original study).
- 2Enter the platelet count. Enter the platelet count in ×10⁹/L.
- 3Read the index. The tool computes APRI and shows where it falls against the published thresholds.
Medical disclaimer: This is general health information, not medical advice. It does not diagnose or treat any condition, and the results are estimates based on public reference formulas. Always consult a qualified doctor about your individual health. If you think you may have a medical emergency, contact your local emergency services immediately.
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Book a consultationFrequently asked questions
What is a normal APRI?⌄
An APRI of 0.5 or less suggests significant fibrosis is unlikely. Values above 0.7 increasingly suggest at least moderate fibrosis, and above 1.0 raise the possibility of cirrhosis in chronic hepatitis C.
Can APRI replace a liver biopsy or scan?⌄
No. APRI is a screening index from routine bloods. Indeterminate or high values usually prompt further assessment such as elastography or specialist review; it does not replace these.
Which AST upper limit of normal should I use?⌄
Use your laboratory’s reference. The original Wai 2003 study used 40 IU/L. The result depends on this value, so it is entered explicitly.
Sources & validation
This calculator reproduces the published APRI score, validated for significant fibrosis or cirrhosis in chronic liver disease (hepatitis C).
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