GPT and hepatitis C virus infection: Serum alanine aminotransferase (ALT) level testing was initially introduced in blood services as a surrogate marker for what was then called “non-A non-B” hepatitis and was later identified as hepatitis C. Elevated ALT level in an asymptomatic donor may constitute an unspecific marker for a wide range of active and potentially transmissible viral hepatitis infections (i.e., HBV, HAV, HCV, and HEV) (23).