FIB-4 and APRI Calculator

Use this calculator to obtain three common non-invasive fibrosis ratios from one blood panel. Enter age in years, AST and ALT in U/L, and the platelet count in ×10⁹/L (the same figure often printed as ×10³/µl). This is not a biopsy, an elastography reading, or a treatment decision.

FIB-4 = (age × AST) ÷ (platelets × √ALT). APRI = (AST ÷ ULN ÷ platelets) × 100, with the AST upper limit of normal fixed at 40 U/L. The AST/ALT ratio is AST ÷ ALT. Published FIB-4 cut-offs are often around 1.3 to rule out advanced fibrosis and 2.67 to suggest it in NAFLD; APRI uses different tables. Age, acute hepatitis, and thrombocytopenia change how the numbers read.

Age: Age in years.

AST: Aspartate aminotransferase, in U/L.

ALT: Alanine aminotransferase, in U/L.

Platelets: Platelet count in ×10⁹/L.

FIB-4: Fibrosis-4 index.

APRI: AST-to-platelet ratio index, ULN 40.

AST / ALT: Aminotransferase ratio.