You can also do a stool test through EnteroLab.com - this test can detect celiac or gluten sensitvity within 1 year of starting a gluten free diet, so unlike the blood tests, it does not require you to go back to eating gluten to get accurate results. You can also do the Celiac gene test through this lab, and it does not require a doctor in order to get it done...you can do it yourself at home (you just collect the sample and send it back in the special kit they send you).
Corn flakes may be cross-contaminated with gluten, or if they have malt in them, that is also derived from a gluten grain (barley, usually).
Also, yeast is a likely sensitivity for many with Crohn's, so yes, it is possible you will need to avoid or limit yeast intake.
I hope this helps...good luck,
Chronic Lyme Disease, Bartonella (clinical dx only), Gluten & Sulfite Sensitivity, Many Food/Inhalant/Medication/Chemical Allergies & Intolerances, Asthma, Gut issues (dysmotility, non-specific inflammation), UCTD ("Secondary Lupus-Like Syndrome"), Osteoporosis, chronic Lymphopenia, etc.; G-Tube; Currently on TPN due to bowel problems.
Meds: IV Cipro, Heparin (to flush PICC line), Singulair, Claritin, Domperidone, Colloidal Silver (topically & nasally), probiotics, Milk Thistle, Magnesium, homeopathy.