APRI Calculator (AST to Platelet Ratio Index)
Estimate the likelihood of significant liver fibrosis and cirrhosis with the APRI — the AST-to-platelet ratio index — a simple non-invasive score from two routine blood tests. It is recommended by the WHO to assess fibrosis in chronic hepatitis where elastography is not available, and complements the FIB-4 index. Enter the AST, its laboratory upper limit of normal (usually 40) and the platelet count.
About APRI
APRI = (AST ÷ upper limit of normal) × 100 ÷ platelets, a non-invasive marker of liver fibrosis using routine tests, endorsed by the WHO for hepatitis where elastography is unavailable. Source: Wai C-T et al., Hepatology 2003;38(2):518–526.
Frequently asked questions
What is the APRI formula?
APRI = (AST ÷ AST upper limit of normal) × 100 ÷ platelet count (in ×10⁹/L). Most laboratories and studies use an AST upper limit of normal of 40 U/L. For example, an AST of 80 with an upper limit of 40 and a platelet count of 100 gives APRI = (80/40) × 100 ÷ 100 = 2.0.
What do the APRI cut-offs mean?
For cirrhosis, an APRI below 0.5 has a high negative predictive value and helps rule it out, while a value above 1.0 raises concern and above 2.0 is the WHO threshold used to diagnose cirrhosis in hepatitis C, with high specificity. For significant fibrosis, a value above 0.7 is a common threshold. Values in between are indeterminate and usually prompt another test such as elastography.
What is APRI used for?
APRI is a low-cost, non-invasive way to assess liver fibrosis in chronic hepatitis B and C, using tests that are already routine. The WHO recommends it in settings without access to elastography or biopsy. It is often used alongside the FIB-4 index; the two agree closely and either can triage who needs specialist assessment.
How does APRI compare with FIB-4?
APRI and FIB-4 are both simple blood-based fibrosis scores. FIB-4 adds age and ALT and tends to perform slightly better for advanced fibrosis, while APRI is even simpler, needing only AST and platelets. Many clinicians calculate both; agreement between them increases confidence, and disagreement or an indeterminate result points toward elastography.
What can make APRI misleading?
Anything that changes AST or platelets independently of fibrosis — acute hepatitis or a flare (raising AST), alcohol, haemolysis, or a low platelet count from another cause — can shift the result. APRI estimates probability rather than staging fibrosis precisely, so it supports but does not replace elastography, imaging and clinical judgement. This calculator is an educational reference, not medical advice.
This is a reference tool, not a diagnosis or medical advice. Results depend on the laboratory, assay and clinical context, and reference intervals vary between labs and by age and sex — always read your result against the range printed on your own report and discuss it with a qualified healthcare professional.
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