APRI Calculator

Q: What is the APRI formula?

APRI = ((AST ÷ AST upper limit of normal) × 100) ÷ platelet count (×10⁹/L). AST is entered in U/L, the upper limit of normal is lab-specific (typically around 40 U/L), and platelet count is entered in ×10⁹/L.

Q: What is the AST upper limit of normal (ULN)?

The AST upper limit of normal is the top of the reference range your lab reports for AST, typically around 40 U/L but it varies by laboratory and assay. Use your own lab's reported ULN for the most accurate APRI.

Q: What do APRI cutoffs mean?

An APRI below 0.5 makes significant fibrosis unlikely. An APRI at or above 1.5 is associated with cirrhosis. Values in between (0.5 to 1.5) are indeterminate and don't reliably rule fibrosis in or out. These cutoffs were validated primarily in patients with chronic hepatitis C.

Q: How does APRI compare to FIB-4?

FIB-4 adds patient age and ALT to the calculation and is generally considered more externally validated across a broader range of liver disease etiologies, including NAFLD and hepatitis B, whereas APRI was originally derived and validated primarily in hepatitis C.

Q: What units does platelet count use?

Enter platelet count in ×10⁹ cells per liter (×10⁹/L), the standard SI unit reported on most complete blood count (CBC) panels. This is numerically equivalent to the older ×10³/µL convention some labs still use.

Q: Is confirmatory testing needed after an APRI result?

Yes, especially for indeterminate results. APRI is a non-invasive screening index, not a diagnosis. Elastography (such as FibroScan) or liver biopsy are typically used to confirm fibrosis stage when APRI is indeterminate or when the clinical picture is uncertain.

Range	APRI
Low — fibrosis unlikely	< 0.5
Indeterminate	0.5 – 1.5
High — cirrhosis likely	≥ 1.5

	APRI	FIB-4
Inputs	AST, AST ULN, platelets	Age, AST, ALT, platelets
Formula	((AST ÷ ULN) × 100) ÷ platelets	(Age × AST) ÷ (platelets × √ALT)
Age-adjusted	No	Yes
Original validation	Chronic hepatitis C	HIV/hepatitis C co-infection, later broadened
Cross-etiology validation	Less established outside hepatitis C	Generally more externally validated (HCV, HBV, NAFLD)
Role	Simple, lab-only fibrosis screen	Widely used non-invasive fibrosis screen, often paired with APRI

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Walk-through

How to Use This Calculator

3 steps

1

Enter your AST and its upper limit of normal

Enter the AST (aspartate aminotransferase) result in U/L. The AST Upper Limit of Normal (ULN) field is pre-filled with 40 U/L, a common default — replace it with your own lab's reported reference-range ceiling for the most accurate result, since ULN varies by lab and assay.

2

Enter the platelet count

Enter the platelet count in ×10⁹ cells per liter (×10⁹/L), the standard unit reported on most complete blood count (CBC) panels. The calculator updates instantly as you type.

3

Read the APRI value and interpretation

The calculator computes APRI = ((AST ÷ ULN) × 100) ÷ platelets and classifies it — low (fibrosis unlikely, <0.5), indeterminate (0.5–1.5), or high (cirrhosis likely, ≥1.5). Check the Interpretation tab to see your value highlighted against every range, and the vs FIB-4 tab to compare APRI with the other widely used non-invasive fibrosis index.

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Reference

Formula & Methodology

1 formula

APRI

APRI = ((AST ÷ AST ULN) × 100) ÷ Platelet count

AST is entered in U/L, the AST upper limit of normal (ULN) is your lab's reference-range ceiling in U/L (typically around 40 U/L but lab-specific), and platelet count is entered in ×10⁹/L. Wai CT et al. first described and validated APRI in 2003 as a simple, biopsy-free fibrosis screen built entirely from routine labs.

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High YMYL

Trust, Methodology & Sources

Reviewed by Calculover Clinical Team · Updated 2026-07-23 · 2 sources

Editorial accountability

Author: Calculover Clinical Team - Clinical content team

Owner: Calculover Editorial - Editorial oversight

Reviewer: Calculover Clinical Team - Clinical reviewer

Last reviewed: 2026-07-23

Last verified: 2026-07-23

Data effective: 2026-07-23

Methodology

Implements APRI as described by Wai CT, Greenson JK, Fontana RJ, et al., Hepatology. 2003;38(2):518-526: APRI = ((AST ÷ AST upper limit of normal) × 100) ÷ platelet count (×10⁹/L), interpreted against a low range (<0.5, fibrosis unlikely), an indeterminate range (0.5-1.5), and a high range (≥1.5, associated with cirrhosis) drawn from the original validation cohort.

Assumption: AST, its upper limit of normal, and platelet count are assumed to come from the same lab draw or a closely timed set of results.

Assumption: The AST upper limit of normal defaults to 40 U/L but is lab- and assay-specific; users should substitute their own lab's reported reference range for the most accurate result.

Assumption: A single APRI value is treated as a screening data point, not a diagnosis — the calculator does not adjust for etiology, comorbidities, or serial trending.

Limitations & guidance

APRI was derived and validated primarily in patients with chronic hepatitis C; its accuracy is less established in other liver disease etiologies such as NAFLD or hepatitis B, where FIB-4 generally has stronger validation.

An indeterminate result (0.5-1.5) does not reliably rule fibrosis in or out and typically requires a confirmatory test such as elastography or biopsy.

Results are for clinical decision support and education only and do not replace a treating clinician's full assessment.

Professional guidance: This calculator is for clinical decision support and educational purposes only and is not a substitute for professional medical judgment, diagnosis, or treatment. Always consult a qualified clinician for patient care decisions.

Primary sources

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.

MDCalc. AST to Platelet Ratio Index (APRI).

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Glossary

Key Terms Explained

6 terms

APRI The AST to Platelet Ratio Index — a non-invasive score, ((AST ÷ ULN) × 100) ÷ platelet count, used to screen for liver fibrosis or cirrhosis without a biopsy.

AST to platelet ratio The underlying relationship APRI is built on: AST tends to rise and platelet count tends to fall as liver fibrosis progresses, so their ratio increases with more advanced fibrosis.

Liver fibrosis The buildup of scar tissue in the liver in response to chronic injury (such as viral hepatitis, alcohol use, or fatty liver disease). Fibrosis is staged from none/mild to advanced (cirrhosis).

Cirrhosis The most advanced stage of liver fibrosis, characterized by extensive scarring that impairs liver function and structure. An APRI at or above 1.5 is associated with cirrhosis in the original validation cohort.

Hepatitis C A viral infection that causes chronic liver inflammation and, over years, can progress to fibrosis and cirrhosis. APRI was originally derived and validated primarily in patients with chronic hepatitis C.

ULN (upper limit of normal) The top of a lab's reference range for a given test — here, for AST. ULN is lab- and assay-specific, commonly around 40 U/L, and should be taken from the same lab report as the AST value.

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Scenarios

Real-World Examples

3 worked examples

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Low — fibrosis unlikely

AST 25 U/L, ULN 40 U/L, platelets 250 ×10⁹/L

AST 25 U/L AST ULN 40 U/L Platelets 250 ×10⁹/L

((25 ÷ 40) × 100) ÷ 250 = 0.25. An APRI of 0.25 is below 0.5, making significant fibrosis unlikely from this result alone.

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Indeterminate

AST 50 U/L, ULN 40 U/L, platelets 180 ×10⁹/L

AST 50 U/L AST ULN 40 U/L Platelets 180 ×10⁹/L

((50 ÷ 40) × 100) ÷ 180 ≈ 0.69. An APRI of 0.69 falls in the indeterminate range (0.5–1.5) — it neither rules significant fibrosis in nor out, and typically prompts a confirmatory test such as elastography.

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High — cirrhosis likely

AST 100 U/L, ULN 40 U/L, platelets 90 ×10⁹/L

AST 100 U/L AST ULN 40 U/L Platelets 90 ×10⁹/L

((100 ÷ 40) × 100) ÷ 90 ≈ 2.78. An APRI of 2.78 is well above the 1.5 cutoff associated with cirrhosis, suggesting a hepatology referral and confirmatory workup.

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Deep Dive

Understanding APRI

3 chapters · 4 min read

APRI — the AST to Platelet Ratio Index — is a simple, biopsy-free score built from two routine lab values that can flag liver fibrosis or cirrhosis. This calculator computes the ratio and classifies it against the low, indeterminate, and high ranges from the original validation study.

How APRI works

APRI combines two signals that both move with worsening liver fibrosis: AST (aspartate aminotransferase), which tends to rise with liver injury, and platelet count, which tends to fall as portal hypertension develops with advancing fibrosis. The formula is APRI = ((AST ÷ AST ULN) × 100) ÷ platelet count, where AST is normalized to the lab's own upper limit of normal before being divided by the platelet count.

Wai CT, Greenson JK, Fontana RJ, et al. first described and validated APRI in a 2003 study of patients with chronic hepatitis C (Hepatology, 2003;38(2):518-526), showing it could predict both significant fibrosis and cirrhosis using only routine labs — no imaging or biopsy required.

Inputs and what they mean

AST (U/L) is a liver enzyme measured on a standard liver panel or comprehensive metabolic panel.

AST upper limit of normal (U/L) is the ceiling of your lab's own reference range for AST — it varies by lab and assay, so use the value printed on your actual lab report rather than a generic default when precision matters.

Platelet count (×10⁹/L) comes from a complete blood count (CBC) and is the same numeric value as the older ×10³/µL convention some labs still report.

Limits and edge cases

APRI is a screening index, not a diagnosis. It was derived and validated primarily in chronic hepatitis C, so its accuracy is less established in other causes of liver disease (such as NAFLD or hepatitis B), where FIB-4 is generally better validated. An indeterminate result (0.5–1.5) is common and does not confirm or exclude significant fibrosis on its own — pairing APRI with another index, elastography, or biopsy is standard practice when the result is indeterminate or the clinical picture is unclear. Conditions unrelated to liver fibrosis (such as other causes of thrombocytopenia or AST elevation) can also shift the ratio.

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Questions

Frequently Asked Questions

6 questions

What is the APRI formula?+

APRI = ((AST ÷ AST upper limit of normal) × 100) ÷ platelet count. AST is entered in U/L, the upper limit of normal is lab-specific (typically around 40 U/L), and platelet count is entered in ×10⁹/L.

What is the AST upper limit of normal (ULN)?+

The AST upper limit of normal is the top of the reference range your lab reports for AST — typically around 40 U/L, but it varies by laboratory and assay. Use your own lab's reported ULN for the most accurate APRI.

What do the APRI cutoffs mean?+

An APRI below 0.5 makes significant fibrosis unlikely. An APRI at or above 1.5 is associated with cirrhosis. Values in between (0.5 to 1.5) are indeterminate and don't reliably rule fibrosis in or out. These cutoffs were validated primarily in patients with chronic hepatitis C.

How does APRI compare to FIB-4?+

FIB-4 adds patient age and ALT to the calculation and is generally considered more externally validated across a broader range of liver disease etiologies, including NAFLD and hepatitis B, whereas APRI was originally derived and validated primarily in hepatitis C.

What units does platelet count use?+

Enter platelet count in ×10⁹ cells per liter (×10⁹/L), the standard SI unit reported on most complete blood count (CBC) panels. This is numerically equivalent to the older ×10³/µL convention some labs still use.

Is confirmatory testing needed after an APRI result?+

Yes, especially for indeterminate results. APRI is a non-invasive screening index, not a diagnosis. Elastography (such as FibroScan) or liver biopsy are typically used to confirm fibrosis stage when APRI is indeterminate or when the clinical picture is uncertain.

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Lab Values

APRI & Interpretation

APRI Reference Ranges

APRI vs the FIB-4 Index

How to Use This Calculator

Enter your AST and its upper limit of normal

Enter the platelet count

Read the APRI value and interpretation

Formula & Methodology

Trust, Methodology & Sources

Key Terms Explained

Real-World Examples

Low — fibrosis unlikely

Indeterminate

High — cirrhosis likely

Understanding APRI

How APRI works

Inputs and what they mean

Limits and edge cases

Frequently Asked Questions

Get a branded PDF of your results

APRI Calculator

Lab Values

APRI & Interpretation

APRI Reference Ranges

APRI vs the FIB-4 Index

How to Use This Calculator

Enter your AST and its upper limit of normal

Enter the platelet count

Read the APRI value and interpretation

Formula & Methodology

Trust, Methodology & Sources

Key Terms Explained

Real-World Examples

Understanding APRI

How APRI works

Inputs and what they mean

Limits and edge cases

Frequently Asked Questions

Get a branded PDF of your results

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