M.C.
Have no medical knowledge of this. Just feel like answering.
My neighbor has Celiacs. He became very sick. Developed hives, rashes and swelling. He lost about 30 lbs before a dermatologist spotted the possible cause and suggested Celiacs.
For me personally, I would think that a stool sample would be a better indicator than the blood. The blood is more of a 'right now' indicator. Whereas the stool shows what and how well something was processed.
Just my two, unlicensed cents.
M.