AST-to-Platelet Ratio Index (APRI) Calculator

Divide AST by the reporting laboratory’s AST upper limit of normal, multiply by 100, and divide by the platelet count expressed as ×10⁹/L. The result is unitless.

Sources: [1]

APRI normalizes AST to the upper limit used by the laboratory that reported that result. Methods and reference intervals differ, so the page does not substitute one universal AST limit.

Sources: [1, 9, 11]

Yes. Use contemporaneous results so that the numerator and denominator describe the same clinical time point. Combining unrelated dates can create a number that the original model did not evaluate.

Sources: [1, 7]

The page accepts ×10⁹/L, ×10³/µL, and cells/µL. Values in ×10⁹/L and ×10³/µL are numerically equivalent; cells/µL are divided by 1,000 before the APRI calculation.

Sources: [1, 9]

A measured AST of zero is accepted mathematically and produces an APRI of zero when the AST upper limit and platelet count are positive. The source result and laboratory context still need review.

Sources: [1, 9]

Wai and colleagues derived APRI in treatment-naive adults with chronic hepatitis C who underwent liver biopsy. Performance in another disease, age group, treatment state, or setting cannot be assumed to match that cohort.

Sources: [1, 2]

The original study evaluated paired low and high thresholds for significant fibrosis and cirrhosis, with indeterminate zones between them. They were probability tools in studied populations, not universal diagnostic boundaries.

Sources: [1, 2, 3]

WHO chronic hepatitis B guidance (2024 detailed criteria; consolidated in the 2026 implementation handbook) uses APRI within a specific treatment-eligibility framework alongside clinical criteria and other routes to eligibility. This calculator does not automatically apply that workflow or recommend treatment.

Sources: [4, 5]

No. Current AASLD-IDSA HCV guidance says APRI or FIB-4 can be helpful when direct biomarkers or elastography are unavailable, but neither is sensitive enough to rule out substantial fibrosis.

Sources: [2, 3, 6]

No. APRI has imperfect sensitivity and specificity, and predictive values vary with disease and population prevalence. Clinical findings, other noninvasive tests, imaging, and sometimes histology remain relevant.

Sources: [2, 3, 7, 8]

WHO chronic hepatitis B guidance uses APRI >0.5 for significant fibrosis (≥F2) and clinical criteria or APRI >1.0 for cirrhosis (F4) in adults and adolescents aged ≥12 years. The adult recommendation is strong with moderate-certainty evidence; the adolescent recommendation is strong with low-certainty evidence. Direct diagnostic-accuracy evidence in adolescents is limited because WHO extrapolates adult evidence. Do not extend these recommendations automatically to children younger than 12, and this calculator does not apply the treatment-eligibility workflow.

Sources: [4, 5]

Yes. Acute inflammation or a flare can raise AST without a corresponding change in fibrosis and may produce a falsely high index. Timing and disease activity matter.

Sources: [7, 9]

Yes. AST is not liver-specific. Strenuous exercise, skeletal-muscle injury, hemolysis, specimen quality, and other nonhepatic sources can raise AST and therefore change APRI.

Sources: [9, 10, 11]

Yes. Infection, medicines, immune or marrow disorders, pregnancy, splenic sequestration, and other conditions can alter the platelet count and therefore the index.

Sources: [7, 8]

No. Those decisions require the applicable disease-specific guideline, clinical assessment, and other evidence. This page only reproduces the APRI arithmetic.

Sources: [4, 6, 7]

APRI combines AST relative to its laboratory upper limit with platelets. The De Ritis ratio divides AST by ALT, while FIB-4 also includes age and ALT. They are distinct models and are not interchangeable.

Sources: [1, 7, 9]