Elevated Gamma GT, but other liver function tests normal?

Hi,

I just got my blood test back and found that I have an extremely high count of Gamma GT (490)--there was also a note saying that they checked it twice. My alkaline phosphatase is also in the high end, but still in normal range (250). However, my bilirubin (total/direct), SGOT, and SGPT are well within normal range.

I have been retested in a different lab (repeat testing of Gamma GT and alkaline phosphatase, as well as Hepatitis) and am still waiting for the results, but should I be concerned? Could it be a fluke? My doctor didn't seem too concerned, but he did suggest an ultrasound once we get the results of my latest blood test.

My total cholesterol is 123 (HDL 32, LDL 82) and my triglycerides is 44. I'm on a moderate diet and exercise program (low-intensity cardio and yoga, daily). I drink once or twice a week and never more than one to two glasses, but I am a smoker. Can this affect the results?

I've also been taking an anti-thyroid agent for my hyperthyroidism (methimazole) for a year now, but if it is that, I'm confused as to why it's only affecting my Gamma GT levels, while everything else appears to be normal.

If anyone can share any insight/experience regarding this problem, I'd appreciate it a lot.
Thanks.