APRI Score Calculator (AST to Platelet Ratio Index)
Non-invasive liver fibrosis estimate with the APRI score — AST relative to its upper limit of normal divided by platelet count — with cut-offs for significant fibrosis and cirrhosis in hepatitis C, hepatitis B and fatty liver.
How it works
APRI = [(AST ÷ AST upper limit of normal) × 100] ÷ platelet count (×10⁹/L)
As the liver scars, hepatocyte injury raises AST while portal hypertension and reduced thrombopoietin lower platelets; the AST-to-platelet ratio index captures both trends in one number that needs only a routine blood count and liver panel. Developed in hepatitis C, it is now used across chronic liver disease and endorsed by the WHO for resource-limited settings. Its strength is ruling out: below 0.5 significant fibrosis is unlikely, and below 1.0 cirrhosis is unlikely. Its weakness is a large indeterminate zone — roughly a third of patients fall between 0.5 and 1.5 — where FIB-4, elastography or a specialist referral is needed. Acute hepatitis, alcohol binges and non-hepatic causes of thrombocytopenia distort it.
Worked example
AST 78 with a lab ULN of 40 and platelets 130: (78/40 × 100) / 130 = 1.50 — advanced fibrosis likely; confirm with FibroScan.
Frequently asked questions
Which ULN should I use?
Your own laboratory’s stated upper reference limit for AST — commonly 35–40 U/L. Using 40 when the lab uses 35 changes the score by about 12%.
APRI or FIB-4?
FIB-4 adds age and ALT and performs slightly better, especially in fatty liver disease; the two agree in most patients and are often reported together.
Related calculators
Clinical decision tool for education and for use by trained clinicians alongside judgement — not a diagnosis and not a substitute for medical assessment. Scores validated in specific populations may not apply to every patient.