How it's calculated
APRI = (AST ÷ AST upper limit of normal) × 100 ÷ platelet count (×10⁹/L). Higher values suggest more significant hepatic fibrosis.
Interpretation
| APRI | Interpretation |
|---|---|
| < 0.5 | Unlikely significant fibrosis |
| 0.5 – 1.5 | Indeterminate |
| > 1.5 | Suggests significant fibrosis/cirrhosis |
Clinical use
- APRI was originally validated in chronic hepatitis C, and is used as a simple, widely-available noninvasive screen where elastography or biopsy aren't readily accessible.
- It performs less well at distinguishing intermediate stages of fibrosis than at the extremes (rules out advanced fibrosis well at low values, and is a reasonable indicator of it at high values).
- The AST upper limit of normal varies between laboratories — always use your own lab's reference value, not a value copied from elsewhere.
- APRI is a screen, not a replacement for liver biopsy or transient elastography (FibroScan) where a precise fibrosis stage genuinely changes management.
Frequently asked questions
What is the APRI score used for?
It's a simple, noninvasive blood-test-based screen for liver fibrosis, using only AST and platelet count, most extensively validated in chronic hepatitis C.
Why does the AST upper limit of normal matter?
The APRI formula expresses AST as a ratio to its upper limit of normal, and this reference value varies between laboratories — using the correct value for your specific lab is important for an accurate result.
Is APRI as accurate as a liver biopsy?
No — it's a noninvasive screening tool, useful for identifying patients unlikely to have significant fibrosis (avoiding unnecessary biopsy) or those likely to have advanced disease, but it doesn't replace biopsy or elastography when a precise fibrosis stage is needed.
Can APRI be used in conditions other than hepatitis C?
It has been studied in other liver diseases (including NAFLD and hepatitis B) with somewhat variable performance — FIB-4 is another simple noninvasive score often used alongside or instead of APRI.
References
- Wai CT, et al. A simple noninvasive index can predict both significant fibrosis and cirrhosis in patients with chronic hepatitis C. Hepatology. 2003;38:518-526.
- Lin ZH, et al. Performance of the aspartate aminotransferase-to-platelet ratio index for the staging of hepatitis C-related fibrosis: an updated meta-analysis. Hepatology. 2011;53:726-736.
- World Health Organization. Guidelines for the Prevention, Care and Treatment of Persons with Chronic Hepatitis B Infection.