Liver enzymes

Liver enzymes are proteins made by liver cells, such as ALT, AST and alkaline phosphatase, whose levels in the blood are measured to detect liver stress or injury.

The liver processes nutrients, drugs and toxins, and when its cells are damaged they leak enzymes into the bloodstream. Alanine aminotransferase and aspartate aminotransferase rise mainly with injury to liver cells, while alkaline phosphatase and gamma-glutamyl transferase rise with obstruction of bile flow. A routine blood panel reports each with a reference range, and mild elevations are common and often temporary, caused by medications, alcohol, fatty liver, viral infection or vigorous exercise.

Liver enzymes are the main safety measure in cannabinoid clinical trials. In studies of the prescription cannabidiol drug, elevations occurred in a minority of participants, more often at higher doses and in those also taking valproate, and they usually resolved when the dose was reduced or stopped; prescribing information recommends checking the enzymes before and during treatment. Similar monitoring is standard in veterinary CBD studies, where alkaline phosphatase increases have been reported in dogs. A high value prompts repeat testing and evaluation of the cause rather than a diagnosis on its own.