Why must I enter the AST upper limit of normal?

APRI normalizes AST to the reporting laboratory's own upper limit. Assays and reference intervals differ, so a single default ULN would not be appropriate for every result.

Can APRI diagnose or exclude cirrhosis?

No. APRI was developed as a noninvasive index in chronic hepatitis C and has imperfect performance. Disease, population, and purpose affect how it is used.

What else can change APRI?

AST can rise from hepatic and nonhepatic causes, while platelet count can change for many reasons unrelated to fibrosis. Other laboratory, imaging, and clinical information remains important.

Educational reference only. Not a diagnostic tool. See full disclaimer.

HepaticAPRI

AST-to-Platelet Ratio Index Calculator

Calculate APRI from AST, laboratory AST ULN, and platelet count.

Content updated: July 18, 2026View sources

AST

U/L

Laboratory AST upper limit of normal

U/L

Platelet count

AST-to-Platelet Ratio Index

—

Noninvasive laboratory index; no fibrosis category is assigned

AST/ULN: — · platelets: — ×10⁹/L

About

The AST-to-Platelet Ratio Index (APRI) is a noninvasive index originally developed in treatment-naive adults with chronic hepatitis C. This page reports the arithmetic without assigning a fibrosis stage.

Formula

APRI = [(AST ÷ laboratory AST ULN) × 100] ÷ platelet count (×10⁹/L)

Interpretation

What the result represents: AST relative to the reporting laboratory upper limit, scaled by platelet count.

Input units: AST and its laboratory ULN use U/L. Platelets may use ×10³/µL, ×10⁹/L, or cells/µL and are normalized to ×10⁹/L.

Worked example: AST 80 U/L, AST ULN 40 U/L, and platelets 200 ×10⁹/L gives APRI 1.00.

Applicable population: Originally derived for chronic hepatitis C; performance and cutoffs differ by liver disease, population, and clinical purpose.

Interpretation limitations: APRI does not by itself diagnose or exclude fibrosis or cirrhosis. AST from nonhepatic causes and platelet changes from other conditions affect the index. Interpret with clinical context, other noninvasive assessment, imaging, and specialist evaluation where appropriate.

References

FAQ

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Disclaimer

Educational and informational reference only. Not intended to replace professional medical advice, diagnosis, treatment, or independent verification.