I have only had the ALT and AST liver tests so don't have personal experience. I have had high readings on one of these tests after I took the maximum dose of a cold medication for a week. It contained Tylenol. I had elevated readings another time after taking Tylenol and have concluded that I need to limit my use of that drug. My readings were only slightly high and your readings on the GGT are very high. Looking online there can be a number of diseases and disorders that cause an elevated GGT so that's an issue for your doctor.