GPT and animal viral hepatitis: These biomarkers form the foundation of ‘Hy’s Law’ in which drug-induced hepatocellular injury is defined as; the presence of a threefold or greater elevation above the upper normal limit (ULN) of ALT or AST compared to control, the elevation of TBIL > 2 times the ULN without initial evidence of cholestasis and, no pre-existing or underlying explanation for the elevation of ALT, AST and TBIL, such as viral hepatitis (US Food and Drug Administration 2009).