Hepatology

APRI Calculator (AST to Platelet Ratio Index)

Noninvasive assessment of liver fibrosis

Primary source: Wai CT et al. Hepatology 2003; 38(2): 318-326

Aleksandr A. Aulov, MD, internal medicine Last clinical review: April 28, 2026

Online calculation

AST

U/L

AST ULN (upper limit of normal)

U/L

Platelet count

10⁹/L

About this score

APRI (AST to Platelet Ratio Index; Wai CT et al., Hepatology 2003) is a simple noninvasive marker of liver fibrosis, particularly in HCV infection. Formula: APRI = (AST/ULN × 100) / platelet count (10⁹/L).

Interpretation: < 0.5 - low probability of significant fibrosis (F2 or greater); 0.5-1.5 - gray zone; > 1.5 - probable significant fibrosis; > 2.0 - high probability of cirrhosis. Sensitivity for significant fibrosis ~77%, specificity ~72%.

The main advantage is accessibility: it uses only AST and platelet count from standard laboratory tests. This makes APRI a valuable screening tool in primary care before referral to more precise methods (FibroScan, FibroTest, biopsy). WHO 2017 guidelines include APRI and FIB-4 as standard noninvasive markers.

When to use

Screening for fibrosis in patients with chronic HCV or HBV.
Initial assessment in hepatic steatosis (NAFLD) - stratification before FibroScan.
Serial monitoring of treatment response (e.g., after successful DAA therapy for HCV).
Resource-limited settings where FibroScan is not available.

Clinical example

Case

45-year-old woman with chronic HCV, genotype 1b, treatment-naive. AST 80 U/L (ULN 40), platelet count 145×10⁹/L.

Calculation

APRI = (80/40 × 100) / 145 = 200 / 145 = 1.38.

Interpretation and management

APRI 1.38 - gray zone between significant fibrosis and normal. Approach: further evaluation with FibroScan or biopsy for precise staging. In parallel, start DAA therapy (priority regardless of stage under current guidelines). After SVR (sustained virologic response), repeat APRI at 12 weeks: a significant decrease is expected.

Limitations and cautions

The gray zone of 0.5-1.5 includes a substantial proportion of patients, who require additional testing.
AST may be elevated for other reasons (myocarditis, muscle injury), skewing the result.
Thrombocytopenia of other etiology (ITP, hypersplenism) increases APRI without fibrosis.
Less accurate in NAFLD - FIB-4 or NFS (NAFLD Fibrosis Score) perform better there.

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Frequently asked questions

APRI vs FIB-4 - which is better?

FIB-4 is more accurate in NAFLD and in older patients. APRI was historically developed for HCV. In practice, both are calculated and compared.

At what APRI value should a patient be referred for FibroScan?

Any value in the gray zone (0.5-1.5) with suspected chronic liver disease is an indication for FibroScan.

Does APRI change after HCV treatment?

Yes, in responders APRI decreases significantly within 12-48 weeks after SVR. Persistently elevated APRI after SVR warrants further evaluation for HCC.

Can APRI be used in children?

Use with caution - dedicated pediatric scales are preferable. The standard APRI has been validated for adults.

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Aleksandr A. Aulov Physician, internal medicine, Sechenov School — independent medical education platform. Calculators are compiled from the original publications and current clinical guidelines. Interpretation thresholds follow the source study unless stated otherwise.

This calculator is intended for healthcare professionals. Do not use it for self-diagnosis or self-treatment. Management decisions are made by the treating clinician based on the full clinical picture of the individual patient.