Celiac Disease testing and diet

Hi everyone,
My rheumy is treating me for Psoriatic Arthritis. I have been on Enbrel for 6+ months. The Enbrel has basically given me my life back. Unfortunately, I have had some recent flare-ups. I thought I would try a gluten-free diet, with the thought that maybe glutens were contributing to my inflammation and joint pain. I have been pretty true to the diet for about a week. I was planning on continuing it because I think it really is helping to reduce some of the inflammation causing my joint pain. However, my friend just told me that there is a blood test that can screen for Celiac Disease and I have 2 concerns: #1 if I try to have the blood test done, after being on the gluten-free diet (even though it is only a week,) will test results yield a false negative? and #2: if I really do have an intolerance to gluten and I go back on a regular non-gluten-free diet, in order to get accurate blood test readings, will that make me sick or cause damage?