My daughters pediatrician wants to check her for diabetes but said that he isn't going to do the 4 hour glucose tolerance test because in people with celiac the results are "flat". I asked him what that meant and he just repeated that the results would be flat and not accurate. He is instead doing a first thing in the morning blood draw to check her sugar. Has anyone heard of this? What does flat mean? Will the other test be accurate?

I don't know what he is referring to with the glucose tolerance test. I do know I have had lots of them over the years though.
The fasting morning sugar is a good measure. He should be doing an A1C at the same time, this measures the average blood sugar over a three month period. The morning blood sugar can be elevated if someone is ill, in that case the A1C can make the difference between a premature diagnosis of diabetes and the need to recheck at a later date.