Thanks for your input. I don't take the maximum of Tylenol per day and have taken two at night for 30 years or more so it seems very doubtful that's playing a part in this sudden rise in GGT. My doctor concurs. Since Prednisone as well as autoimmune diseases can cause high GGTs and ALK, I was merely wondering if anyone else had experienced this. As a nurse of 40+ years, I don't look for medical advice in a forum.