My regular doctor wouldn't do it (no surprise there). So I had it done through this lab which partners with local labs so you just walk in and have blood drawn. Easy enough, I may have my questions about accuracy but for me it seems to be on the mark . http://www.pyroluriatesting.com/?page=shop/browse&category_id=1
And I good way to explain it is for someone who is very allergic to bee stings they get an epi-pen which is just adrenaline because adrenaline breaks down histamine. Ie if your body is not breaking down histamine it needs to release adrenaline. I am unsure if I have a hidden food allergy or if I under-methylate. So far trying to follow this diet (its not an easy one though!) http://www.urticaria.thunderworksinc.com/pages/lowhistamine.htm
I have only been taking methionine in oral form, no problems yet, but only had it about 5 days.