Calculate the AST-to-platelet ratio index (APRI) from AST, the reporting laboratory’s AST upper limit of normal, and a platelet count. Check the unit and use values from the same blood draw.
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Formula and example
APRI = (AST ÷ laboratory AST upper limit of normal) ÷ platelets (10⁹/L) × 100. With AST 80 U/L, an upper limit of 40 U/L and platelets 200 ×10⁹/L, the score is (80 ÷ 40) ÷ 200 × 100 = 1.00. A platelet count of 200 ×10³/µL is the same value; select /µL for a raw count such as 200,000/µL.
Interpretation and scope
In its chronic hepatitis C guidance, WHO gives APRI 0.5 as a lower and 1.5 as a higher cut-off for significant fibrosis (METAVIR ≥F2). A score between them is inconclusive on its own; values outside the range do not prove or exclude disease. Cirrhosis assessment uses different cut-offs and should not be confused with these significant-fibrosis references.
Other causes of high AST or low platelets can change APRI. Your clinician should consider the cause of liver disease and the full clinical picture.
What to do next
Confirm the laboratory AST upper limit, platelet unit and whether the tests came from the same blood draw. Discuss other assessment, such as FIB-4 or liver elastography, with your clinician when appropriate.
Frequently asked questions
What if I do not know the AST upper limit?
Look for the top of the AST reference range on your laboratory report. Reference ranges can differ, so avoid guessing.
Does changing the platelet unit change the result?
Correctly converted values yield the same score: 200 ×10⁹/L, 200 ×10³/µL and 200,000/µL all equal 200 ×10⁹/L.
Can APRI diagnose cirrhosis?
No. Performance varies by population and clinical setting. A clinician may need to review other blood tests and non-invasive assessments.
Related tools and records
FIB-4 liver fibrosis calculator · Health records and visit preparation · All calculators
Sources
WHO 2018 chronic hepatitis C guidance: APRI cut-offs · Wai et al. (2003): original APRI study · University of Washington Hepatitis C Online: APRI
Sources reviewed September 30, 2026. General information, not a diagnosis or substitute for clinical care. No independent clinician review is claimed.