APRI Calculator | AST-to-Platelet Ratio Index

APRI Calculator

AST (U/L)

AST Upper Limit of Normal (U/L)

Standard ULN is 40 U/L in most laboratories. Use your lab's reference range.

Platelet count (10⁹/L)

Enter in 10⁹/L. E.g. if report says 1.9 lakh, enter 190.

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Enter values above

Formula

APRI = (AST / AST-ULN) ÷ Platelet count (10⁹/L) × 100
AST in U/L · ULN typically 40 U/L · Platelets in 10⁹/L

APRI Score	Interpretation	Sensitivity / Specificity
< 0.5	Low probability of significant fibrosis (F0–F1)	Sens ~87% (ruling out F2+)
0.5–1.5	Indeterminate — fibrosis present but stage uncertain	—
≥ 1.5	Significant fibrosis likely (F2–F4)	Spec ~93%
≥ 2.0	Cirrhosis probable (F4)	Spec ~91%

Performance characteristics are derived primarily from HCV cohorts (Wai 2003); performance in NAFLD is somewhat lower.

APRI has been recommended by WHO (2014, 2016) guidelines as a first-line fibrosis assessment tool in HCV — particularly in resource-limited settings where FibroScan is unavailable.
In chronic HCV: APRI <0.5 excludes significant fibrosis; APRI ≥2.0 makes cirrhosis highly likely, guiding treatment urgency and complication surveillance.
APRI is less accurate than FIB-4 or liver stiffness measurement (LSM) for NAFLD — AASLD guidelines now recommend FIB-4 as the preferred first-line tool in NAFLD.
After successful HCV treatment (SVR), AST normalises rapidly while platelet count may lag — repeat APRI at 24 weeks post-SVR for accurate fibrosis reassessment.
Limitations: APRI is affected by any cause of elevated AST (muscle, haemolysis, thyroid, medication) or thrombocytopenia (hypersplenism, immune causes). Clinical context is always required.

Wai CT, 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.
WHO Guidelines. Guidelines for the screening, care and treatment of persons with chronic hepatitis C infection. Updated version. 2016.
Lin ZH, et al. Performance of the aspartate aminotransferase-to-platelet ratio index for the staging of hepatitis C-related fibrosis. Hepatology. 2011;53(3):726–736.