APRI Calculator

AST to Platelet Ratio Index — a simple, noninvasive estimate of liver fibrosis likelihood from two routine blood values. Free, private, 100% in your browser.

Educational tool only — not medical advice. APRI screens and stratifies risk; it does not diagnose fibrosis. Diagnosis needs full clinical evaluation (e.g. elastography or biopsy). Discuss results with a clinician.

Calculate your APRI score

Enter the values from your lab report. Use your lab's own AST upper limit of normal (ULN).

AST (IU/L) Aspartate aminotransferase from your blood test.

AST upper limit of normal (ULN) Your lab's reference range top value. Default 40.

Platelets (×10⁹/L) Same as K/µL or ×10³/µL on most reports.

Interpreting the score

Classic cutoffs validated for chronic hepatitis C (Wai et al., 2003). Cutoffs vary by liver disease cause — see the note below.

< 0.5

Significant fibrosis unlikely. A low score is reassuring but does not rule out liver disease on its own.

0.5 – 1.5

Indeterminate gray zone. Many people land here; this result calls for clinical review and usually further testing.

> 1.5

Significant fibrosis or cirrhosis likely. Needs prompt clinical evaluation.

A note on cutoffs by cause

The 0.5 / 1.5 thresholds were validated mainly in chronic hepatitis C. Optimal cutoffs differ for chronic hepatitis B, fatty liver disease (MASLD/NAFLD), and alcohol-related liver disease, and study results vary. Treat any cutoff as a screening guide tied to the specific condition, not a universal rule.

Worked examples

Tap one to load it into the calculator.

Low score — 0.30

AST 30, ULN 40, platelets 250 → ((30/40)×100)/250 = 0.30 → significant fibrosis unlikely.

Gray zone — 1.33

AST 80, ULN 40, platelets 150 → ((80/40)×100)/150 = 1.33 → indeterminate.

High score — 3.33

AST 120, ULN 40, platelets 90 → ((120/40)×100)/90 = 3.33 → significant fibrosis / cirrhosis likely.

Scope boundary: APRI vs FIB-4

This tool calculates APRI only. Here is how it differs from its closest sibling score.

	APRI (this tool)	FIB-4
Inputs	AST, AST ULN, platelets	Age, AST, ALT, platelets
Formula	((AST/ULN)×100)/platelets	(age×AST)/(platelets×√ALT)
Best validated in	Chronic hepatitis C	Broader use, incl. fatty liver disease and older adults
Age adjustment	None	Built in (age is a factor)
Use together?	Yes — they are complementary. Discordant results (one low, one high) usually mean further testing is needed.

The formula

APRI = ((AST / ULN_AST) × 100) / platelet count (×10⁹/L)

Frequently asked questions

What is the APRI score?

APRI stands for AST to Platelet Ratio Index. It is a simple, noninvasive score that estimates the likelihood of significant liver fibrosis using two routine blood values: AST (aspartate aminotransferase) and platelet count. It was first validated by Wai and colleagues in 2003 in people with chronic hepatitis C. It is a screening and risk-stratification aid, not a diagnosis.

How is the APRI score calculated?

APRI = ((AST / ULN of AST) x 100) / platelet count (in x10^9/L). First divide the patient's AST by the upper limit of normal (ULN) for AST at your lab, multiply by 100, then divide by the platelet count. For example, AST 80 with a lab ULN of 40 and platelets 150 gives ((80/40) x 100) / 150 = 1.33.

How do I interpret the APRI score?

Using the classic hepatitis C cutoffs: below 0.5, significant fibrosis is unlikely; 0.5 to 1.5 is an indeterminate gray zone; above 1.5, significant fibrosis or cirrhosis is likely. Scores in the gray zone are common, so an indeterminate result should be followed by clinical review and often additional testing such as elastography.

Do APRI cutoffs differ for hepatitis B, fatty liver, or other causes?

Yes. The 0.5 and 1.5 cutoffs were validated mainly for chronic hepatitis C, and optimal thresholds vary by liver disease cause. For example, some studies in chronic hepatitis B use different cutoffs, and performance in fatty liver disease (MASLD/NAFLD) or alcohol-related disease can differ. Always interpret APRI in the context of the specific condition and your clinician's guidance.

What is the difference between APRI and FIB-4?

Both are noninvasive blood-based fibrosis scores, but they use different inputs. APRI uses only AST and platelets. FIB-4 adds age and ALT to the calculation (age x AST) / (platelets x sqrt(ALT)), so it tends to perform better in older adults and is more widely used in fatty liver disease. They are complementary, not interchangeable: a low score on one and high on the other usually means further testing is needed.

What ULN value should I use for AST?

Use the upper limit of normal printed on your own lab report, because reference ranges differ between laboratories and assays. A common default is 40 IU/L, but yours may be 33, 45, or another value. Using the wrong ULN shifts the whole score, so matching your lab's range matters.

Which platelet units does the APRI formula need?

The formula expects platelets in x10^9/L. That is the same as K/uL or x10^3/uL, which is how many lab reports print it (for example, 150 K/uL = 150 x10^9/L). If your report uses a different unit, convert it first.

Is there a normal APRI range?

APRI does not really have a 'normal range' like a blood count does. It is a risk score, not a physiological measurement. Lower is generally reassuring and higher raises concern for fibrosis, but there is no single value that is 'normal' for everyone — interpretation always depends on cutoffs validated for the underlying liver condition.

What can make the APRI score misleading?

Anything that raises AST or lowers platelets for reasons other than fibrosis can distort APRI: acute hepatitis flares, heavy alcohol use, muscle injury, certain medications, and conditions that lower platelets such as ITP or splenic disorders. APRI also cannot reliably distinguish intermediate stages of fibrosis — that is exactly what the 0.5-1.5 gray zone reflects.

Can APRI replace a liver biopsy or FibroScan?

No. APRI is a triage tool. Biopsy remains the reference standard for staging fibrosis, and vibration-controlled transient elastography (often called FibroScan) measures liver stiffness directly. In practice, clinicians often combine APRI or FIB-4 with elastography, and only pursue biopsy when results are discordant or a precise stage is needed for treatment decisions.

Free tool by NRTechStudio

APRI Calculator

Calculate your APRI score

Interpreting the score

A note on cutoffs by cause

Worked examples

Scope boundary: APRI vs FIB-4

The formula

Frequently asked questions

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