APRI Score Calculator — AST to Platelet Ratio Index
The AST to Platelet Ratio Index (APRI) is a validated non-invasive biomarker for liver fibrosis in chronic liver disease, particularly hepatitis C and NAFLD. Developed by Wai et al. (2003).
About
The AST to Platelet Ratio Index (APRI) was developed by Wai et al. in 2003 as a simple, inexpensive, and readily available non-invasive test for predicting significant fibrosis and cirrhosis in patients with chronic hepatitis C. The index uses only two laboratory values — AST and platelet count — making it one of the simplest fibrosis biomarkers. APRI has been validated across multiple etiologies of chronic liver disease including hepatitis B, NAFLD, and alcoholic liver disease. The test calculates the ratio of AST to the upper limit of normal (typically 40 U/L) divided by platelet count (×10⁹/L), multiplied by 100. An APRI <0.5 reliably excludes cirrhosis (F0-F1) with a negative predictive value of 86-97%. An APRI >1.5 is highly specific for cirrhosis (F3-F4) with a positive predictive value of 88-100%. The indeterminate range (0.5-1.5) requires further evaluation with elastography or other non-invasive tests. APRI has been endorsed by the World Health Organization (WHO) for use in resource-limited settings where advanced imaging may not be available.
Formula
APRI = (AST / ULN) / Platelet Count × 100
APRI uses two laboratory parameters: AST (aspartate aminotransferase in U/L) and Platelet count (×10⁹/L). ULN (upper limit of normal) for AST is typically 40 U/L. The AST/ULN ratio is calculated first, then divided by the platelet count, and multiplied by 100. The resulting score ranges from 0 to typically 10+. An APRI <0.5 indicates low risk of cirrhosis (F0-F1), 0.5-1.5 is indeterminate, and >1.5 indicates high risk of cirrhosis (F3-F4). The test is most accurate at the extremes of the range, with the indeterminate zone requiring further investigation.
Score Interpretation
The APRI score is one of the simplest and most accessible non-invasive biomarkers for liver fibrosis. Its major clinical advantage is that it requires only two routinely available laboratory tests (AST and platelet count), making it ideal for resource-limited settings. The WHO has endorsed APRI for use in hepatitis C elimination programs worldwide, particularly in low- and middle-income countries where FibroScan and other advanced fibrosis assessment tools may not be available. The meta-analysis by Lin et al. (2011) including over 6,000 patients demonstrated that APRI has an AUROC of 0.77 for significant fibrosis and 0.84 for cirrhosis. The major limitation of APRI is the indeterminate range (0.5-1.5) which encompasses approximately 30-60% of patients in various studies, requiring further evaluation. APRI performs less well in patients with acute hepatitis, thrombocytopenia from other causes, or conditions that elevate AST independent of liver fibrosis (e.g., hemolysis, myopathy). When combined with FIB-4, the diagnostic accuracy for excluding advanced fibrosis improves significantly.
Low risk of cirrhosis (F0-F1) — 0–0.49
APRI <0.5. Low probability of significant fibrosis or cirrhosis. Negative predictive value 86-97%.
Management: No further fibrosis evaluation required. Reassess annually with liver enzymes and APRI.
Indeterminate zone — 0.5–1.5
APRI 0.5-1.5. Indeterminate probability of cirrhosis. Further evaluation recommended.
Management: Perform transient elastography (FibroScan) or MRE. Consider liver biopsy if non-invasive tests are discordant. Reassess APRI every 6-12 months.
High risk of cirrhosis (F3-F4) — 1.51+
APRI >1.5. High probability of advanced fibrosis (F3-F4). Positive predictive value 88-100%.
Management: Refer to hepatology. Perform transient elastography for confirmation. Screen for varices and HCC. Start HCC surveillance.
Reference Ranges
| Population | Normal Range | Notes |
|---|---|---|
| Adults with chronic liver disease (HCV, HBV, NAFLD) | <0.5 — Low risk (F0-F1) | NPV 86-97% for excluding cirrhosis |
| Adults with chronic liver disease | 0.5-1.5 — Indeterminate | Requires further evaluation with elastography |
| Adults with chronic liver disease | >1.5 — High risk (F3-F4) | PPV 88-100% for cirrhosis |
Dr. Khaled Hassan
Dr. Khaled is a cardiology consultant with experience in acute cardiac care.
View medical review board & editorial policy →Example Calculation
A 45-year-old patient with chronic hepatitis C undergoes pre-treatment assessment. Labs: AST 85 U/L, Platelet count 150 ×10⁹/L. ULN for AST = 40 U/L. APRI = (85/40) / 150 × 100 = 2.125 / 150 × 100 = 1.42. This score falls in the indeterminate zone (0.5-1.5). Further evaluation with FibroScan is recommended. If FibroScan shows liver stiffness >12.5 kPa, advanced fibrosis (F3-F4) is likely and the patient should be referred for HCC surveillance and varices screening.
Related Conditions
Common Mistakes
Using APRI in patients with acute hepatitis or acute liver injury
APRI is validated for chronic liver disease. Acute AST elevation from hepatitis flare, drug-induced liver injury, or ischemic hepatitis will falsely elevate the AST numerator and give an overestimated APRI score. Perform APRI when liver enzymes have stabilised.
Not accounting for the ULN reference value used by the local laboratory
APRI requires dividing AST by the upper limit of normal (ULN). Different laboratories may have different ULN values for AST (ranging from 30 to 50 U/L). Always verify the local laboratory's reference range and use the correct ULN value in the calculation.
Interpreting indeterminate APRI as definitive evidence of significant fibrosis
APRI 0.5-1.5 is an indeterminate range. Approximately 30-60% of patients fall into this category. An indeterminate APRI does not confirm or exclude advanced fibrosis and must be followed by elastography or other non-invasive testing before clinical decisions are made.
Frequently Asked Questions
What is the diagnostic accuracy of APRI for cirrhosis?
Can APRI be used for monitoring treatment response?
How does APRI compare to FIB-4?
References
- Wai CT, Greenson JK, Fontana RJ, et al. A simple noninvasive index can predict both significant fibrosis and cirrhosis in patients with chronic hepatitis C. Hepatology. 2003;38(2):518-526. PubMed
- Lin ZH, Xin YN, Dong QJ, 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(3):726-736. PubMed
- World Health Organization. Guidelines for the care and treatment of persons diagnosed with chronic hepatitis C virus infection. Geneva: WHO; 2018.
- European Association for the Study of the Liver. EASL Clinical Practice Guidelines on non-invasive tests for evaluation of liver disease severity and prognosis — 2021 update. J Hepatol. 2021;75(3):659-689. PubMed