You DO NOT have to eat gluten to be tested for Celiac! Don't eat gluten.
A CELIAC PANEL is a DNA test which is accurate for doctor to determine if you are a celiac. Celiac disease is genetic therefore being on a gluten free or gluten diet doesn't not make a difference.
There is a long period of fasting for this test for people like us who suffer from malabsorbtion. It will take 4 larger test tubes of blood. So bring snacks after wards to eat immediately. I was tested positive for celiac disease on a gluten diet and off of gluten, your DNA will show it no matter what. It's always going to be there, unfortunately.