APRI Score

AST to Platelet Ratio Index (APRI) for estimating liver fibrosis and cirrhosis.

Gastroenterology GastroenterologyEvidence-BasedUpdated 2026-07

Clinical decision-support tool for qualified healthcare professionals. Results are not a diagnosis and should not replace professional clinical judgment.

Clinical Notes

The APRI Score is a simple non-invasive marker for liver fibrosis using AST and platelet count.

Calculator Information

Specialty

Gastroenterology

📋 Reference Ranges

Reference ranges for this calculator
Classification	Range
Low Risk	<0.5
Intermediate Risk	0.5–1.5
Significant Fibrosis	>1.5
Suggestive of Cirrhosis	>2.0

What This Calculator Measures

Calculates the AST-to-Platelet Ratio Index (APRI) to estimate the likelihood of significant liver fibrosis and cirrhosis from AST and platelet count, particularly in chronic hepatitis.

How to Use

Enter the patient's AST, the AST upper limit of normal (ULN) for the laboratory, and the platelet count.
Confirm the correct local ULN, because the result scales directly with the ratio AST/ULN.
Interpret the score against the 0.5, 1.5, and 2.0 thresholds.

How the Calculation Works

APRI = [(AST / AST upper limit of normal) x 100] / platelet count (x10^9/L). It compares the AST elevation to the platelet count as a non-invasive marker of hepatic fibrosis.

Variables Explained

AST

Aspartate aminotransferase in U/L, divided by the AST upper limit of normal.

AST Upper Limit of Normal

Laboratory-specific AST upper limit of normal in U/L, used as the denominator of the AST ratio.

Platelet Count

Platelet count in x10^9/L, used as the divisor of the scaled AST ratio.

Interpretation Guide

APRI <0.5 indicates low likelihood of significant fibrosis; 0.5–1.5 intermediate probability; >1.5 significant fibrosis is likely; >2.0 is suggestive of cirrhosis.

Clinical Significance

APRI is a simple, laboratory-only index endorsed by WHO for fibrosis screening in chronic hepatitis, enabling risk stratification in settings without access to elastography.

When It Is Useful

Non-invasive fibrosis estimation in chronic hepatitis, especially HCV
WHO-endorsed fibrosis screening in resource-limited settings
Risk stratification where elastography is unavailable

When It Is Not Useful

Acute hepatitis with a transient AST flare
Thrombocytopenia due to non-portal-hypertension causes
Children and adolescents
When the laboratory AST ULN is uncertain

Common Mistakes

Entering the platelet count in units other than x10^9/L, such as reporting platelets per microliter, which distorts the denominator and can move the score across the 0.5 and 1.5 thresholds.
Calculating APRI during an acute hepatitis flare, because a transient AST elevation inflates the ratio and can mimic significant fibrosis or cirrhosis that is not actually present.
Treating a result in the 0.5 to 1.5 intermediate band as a definitive fibrosis estimate, even though accuracy is lowest in that range and further evaluation is required.

Limitations

The result depends on the chosen AST ULN, which varies between laboratories.
Accuracy is lowest in the intermediate band (0.5–1.5).
Platelet disorders unrelated to fibrosis confound the score.
The model is best validated in chronic hepatitis C.

Worked Example

A 48-year-old man with chronic hepatitis C has AST 120 U/L, an AST upper limit of normal of 40 U/L, and platelets 150 ×10⁹/L.

Inputs:

ast: 120

uln: 40

platelets: 150

Expected Result: APRI = ((120 / 40) × 100) / 150 = 2.0 — significant fibrosis is likely, bordering the cirrhosis threshold (>2.0).

Evidence & References

Source:: Hepatology Literature
Content updated:: 2026-08

Wai CT, et al. Hepatology. 2003;38:518-526.

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. (Original model)

Frequently Asked Questions

Which AST upper limit of normal should I enter?

Enter the upper limit of normal from your own laboratory, since APRI divides the patient's AST by that value before scaling by 100 and the platelet count. Different laboratories use different ULNs, and the score shifts accordingly. If the laboratory ULN is uncertain, the result should not be used for fibrosis decision-making.

Can APRI be used in patients with hepatitis B?

APRI is best validated in chronic hepatitis C and is endorsed by WHO for fibrosis screening in resource-limited settings, including chronic viral hepatitis more broadly. It should not be used during acute hepatitis with a transient AST flare, in children, or when thrombocytopenia arises from causes unrelated to portal hypertension, since those situations confound the score.

What should I do when APRI is between 0.5 and 1.5?

An intermediate result does not resolve the fibrosis question on its own, because accuracy is lowest in the 0.5 to 1.5 range. Patients in this band should proceed to further evaluation, such as elastography where available, or other confirmatory assessment, rather than being labeled as having or not having significant fibrosis based on APRI alone.

Disclaimer: This calculator is intended for educational and clinical decision support purposes only. APRI is a screening index; fibrosis stage should be confirmed with further testing when clinically indicated.