APRI Calculator

Calculate the AST to Platelet Ratio Index for a noninvasive estimate of liver fibrosis risk from routine laboratory values.

AST to Platelet Ratio Index

Use AST and platelet values from the same blood draw and the laboratory's own AST upper reference limit.

AST Level (U/L)

AST Upper Limit of Normal (U/L)

Platelet Count (10⁹/L)

About the APRI score

The AST to Platelet Ratio Index, abbreviated APRI, is a simple noninvasive marker used to estimate the likelihood of liver fibrosis. It combines aspartate aminotransferase activity with platelet count, two measurements commonly available from routine blood testing. APRI was first studied extensively in chronic hepatitis C and has also been evaluated in hepatitis B and other chronic liver diseases. It can help identify people who may need additional evaluation when specialized imaging or biopsy is not immediately available. The formula divides the patient's AST by the laboratory upper limit of normal for AST, multiplies that ratio by 100, and divides by the platelet count expressed in billions per liter. Using the local laboratory's upper reference limit matters because AST ranges differ across instruments, methods, and populations. AST and platelet count should ideally come from the same clinical time point. Entering platelets in another unit without conversion can produce a result that is wrong by several orders of magnitude. Interpretation depends on the disease and cutoff selected. In chronic hepatitis C, values below about 0.5 have often been used to make significant fibrosis less likely, while values above about 1.5 increase concern for significant fibrosis. For cirrhosis, a threshold near 1.0 is sensitive in some settings and a threshold near 2.0 is more specific. The middle ranges are intentionally indeterminate. Cutoffs trade sensitivity against specificity and should be chosen according to current guidance and the clinical question. APRI is not a direct measurement of scar tissue. AST may rise because of acute hepatitis, alcohol exposure, muscle injury, medication, or another transient process. Platelets may fall for reasons unrelated to portal hypertension or chronic liver disease. These factors can elevate the score without advanced fibrosis, while some patients with meaningful fibrosis can still have a low score. Repeating stable laboratory measurements and combining APRI with another validated test can improve assessment. Use the result as one part of a broader liver evaluation that may include history, examination, ALT and other laboratory tests, FIB-4, elastography, ultrasound, and occasionally biopsy. Screening and referral decisions should follow current local guidance. This calculator supports transparent arithmetic and education; a qualified clinician must interpret the score and decide whether further testing or treatment is appropriate.

APRI examples

Laboratory values	APRI	General interpretation
AST 30, upper limit 40, platelets 250	0.30	Lower likelihood of significant fibrosis.
AST 60, upper limit 40, platelets 150	1.00	Indeterminate result that usually needs another assessment.
AST 120, upper limit 40, platelets 100	3.00	Higher likelihood of advanced fibrosis or cirrhosis.

How to calculate APRI

Find the AST result and the laboratory-specific upper limit of normal.
Enter the platelet count in billions per liter from the same clinical time point.
Calculate APRI and verify that every unit matches the field label.
Discuss the result with a clinician alongside other fibrosis tests and clinical findings.

APRI FAQ

What is the APRI formula?

APRI equals AST divided by the AST upper limit of normal, multiplied by 100, then divided by platelet count in billions per liter. The calculation normalizes AST to the reference range before accounting for platelets.

What APRI score suggests liver fibrosis?

A value above 1.5 often raises concern for significant fibrosis in chronic hepatitis C, while a value below 0.5 makes it less likely. Threshold performance varies by disease and population.

Does a high APRI prove cirrhosis?

No. A high result increases suspicion but AST and platelet changes have many possible causes. Confirmation may require elastography, imaging, other blood scores, or specialist evaluation.

Why must I use the laboratory AST upper limit?

Reference limits differ among laboratories and assay methods. Using the printed upper limit ensures the AST ratio is normalized for the test that produced the result.

Can APRI replace a liver biopsy?

Not in every patient or every disease. It can reduce unnecessary invasive testing in selected pathways, but indeterminate or discordant results often need another validated assessment.