Hello, I was diagnosed with Hashimoto's thyroiditis about 3 years ago. At that time I quit gluten and it really helped my symptoms. I hadn't known that I should've tested for celiac before doing so.  Up till recently, gluten would cause my symptoms to flare up, although I never noticed anything with cross contamination, so I wasn't strict about that. But recently, I noticed I could get away with more gluten, and so I decided to do a gluten challenge to see if I had celiac and if I had to be strict. Note that my thyroid antibodies had been decreasing steadily up to this point. My anti-TPO had reached 50 IU/ml from 250 IU/ml (reference range 0-5.6) when I had first been diagnosed. After just a week of the gluten challenge, I measured my thyroid antibodies and they were at 799 IU/ml! I felt fine, but a few days after I started to feel the symptoms. Extreme brain fog, insomnia, diarheaa, fatigue, sleepiness yet cannot sleep, stomachache after eating gluten, nausea, swollen throat (probably due to my thyroid), burping, and gas. I cannot function properly. I'm also worried that I'm killing my thyroid. Should I just quit the challenge? It's been almost two weeks, but the first week I wasn't tracking well, so that's why I didn't want to count it. I can't eat gluten anyway because of my thyroid, but I wanted the diagnosis to know if I should be strict about cross contamination or not.  

You really saved me as I was on day 4 of 3 g per day for 6 weeks. Thank you very much!

Two weeks is the minimum according to the guideline. I would go for four weeks if you can endure it, just to make sure.

Thank you so much! So I can do 10 g worth of gluten in the form of gluten powder per day for two weeks and that should be enough?

It applies to both blood tests and biopsies. Guidelines for the gluten challenge have been revised for the very issue your question raises. It was felt by medical professionals that the longer term but less intense consumption of gluten approach was not proving to be reliable for testing purposes and was resulting in too many false negatives. But do keep in mind that the gluten consumption doesn't have to be in the form of bread slices. It can come in any form: pasta, cake, wraps, etc. Another approach would be to buy gluten powder at a health food store and mix it in a shake. The idea is to get at least 10g of gluten daily, whatever form it comes in.