How this calculator works
APRI combines AST relative to the laboratory's upper limit with platelet count. It was developed for hepatitis C-related fibrosis assessment, and its accuracy depends on the population and other causes of abnormal AST or platelets. Enter the upper limit printed by the laboratory. A score alone cannot confirm or exclude fibrosis. Reverse calculations are algebra, not estimates of missing laboratory measurements. The result is an estimate for information only and is not medical advice.
Formula
APRI = 100 x [AST (U/L) / AST upper limit (U/L)] / platelets (10^9/L). Use the same activity units for AST and its upper limit.
Worked example
AST 80 U/L, upper limit 40 U/L and platelets 200 x 10^9/L give APRI 1. With AST 40 and platelets 200, APRI is 0.5.
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Frequently asked questions
Which platelet unit do I enter?
Use 10^9/L, numerically equal to thousands per microlitre. A count written as 200,000 per microlitre is entered as 200.
Can APRI diagnose cirrhosis?
No. Threshold performance varies and other clinical findings and tests are needed.
What does solving for AST mean?
It returns the value algebraically implied by a chosen score and the other inputs. It does not replace a blood test.