GPT and alcohol abuse: The nonoxidative ethanol metabolites, ethyl glucuronide, and ethyl sulfate, are direct biomarkers of ethanol exposure with a detection window of 2–5 days in urine [8.] Indirect biomarkers for alcohol exposures, such as liver enzymes, gamma glutamyl transferase (GGT), aspartate aminotransferase (AST), and alanine aminotransferase (ALT) can increase as a result of heavy alcohol use; however, these liver enzymes can also increase due to liver injury or disease, unrelated to alcohol use disorders; therefore, these enzymes are not specific for alcohol consumption [5–7].