APRI Calculator
AST-to-platelet ratio index from your laboratory results.
Your laboratory results
Your APRI score
Dimensionless index · not a diagnosis.
How is this calculated?
Measurement guide
AST level
Aspartate aminotransferase (AST) from your blood test (U/L).
Laboratory upper limit
Use the upper limit of normal for AST on your lab report (U/L).
Platelet units
Enter your platelet count and confirm the units (10⁹/L or /µL) from your report.
Calculation & assumptions
APRI = ASTAST upper limitPlatelet count × 100
The aspartate aminotransferase to platelet ratio index (APRI) uses AST in U/L, the laboratory AST upper limit in U/L and platelets in 10⁹/L. The result is a dimensionless index.
Use the laboratory’s own reference limit. Photos show illustrative equipment and report examples, not patient records.
Frequently asked questions
What does the APRI calculate?
APRI is the AST-to-platelet ratio index. It combines AST relative to the laboratory upper limit of normal with platelet count. It is an index used in clinical liver assessment, not a stand-alone diagnosis.
Which values should I enter?
Enter AST in U/L, the AST upper limit of normal printed by the laboratory in U/L, and platelets in the selected unit. Use results from the same blood test.
What formula does this calculator use?
APRI = (AST / AST upper limit of normal) / platelet count in 10⁹/L × 100. The result is dimensionless. Intermediate values are not rounded for calculation.
Why might my result differ from another source?
Different AST upper limits, platelet units, laboratory results or display rounding can change the result. Use the laboratory’s own AST upper limit.
Does the result update automatically?
Yes. Changing any input updates the score, metrics and worked equations immediately. No Apply or Calculate button is required.
More questions (5)
Which platelet unit should I use?
Use the unit on your report. A count of 200 ×10⁹/L equals 200,000/µL. Counts reported as 10³/µL use the same numeric value as 10⁹/L. The unit switch converts the existing value and preserves the result.
Is APRI a diagnosis?
No. APRI alone cannot diagnose or exclude liver fibrosis. Interpretation depends on the underlying condition, the clinical setting and other findings. Discuss results with your clinician.
Is the score a percentage?
No. The multiplication by 100 is part of the APRI formula. An APRI of 0.75 is a dimensionless index, not 0.75% or a probability of disease.
What happens with invalid inputs?
Missing or invalid inputs clear all dynamic results and disable copy and download. AST can be zero; the AST upper limit and platelet count must be positive. Software input bounds are not clinical reference ranges.
Can I use a fixed upper limit of 40 U/L?
Use the upper limit given by the laboratory that performed the AST test. The opening value of 40 U/L is an editable example, not a universal reference limit.
Sources & References
University of WashingtonHepatitis C Online · APRI and clinical limitations.References provide context, not endorsement.
Page information
Updated: October 27, 2026