Doctors will not diagnose celiac based on a blood test alone.   The blood test is step one and the biopsy is step two.   If the biopsy is positive, celiac is diagnosed.  So far, so good, and uncontroversial.

The part that is controversial and that many doctors don't have on their radar screens is that problems with gluten can indicate other issues, such as problems with "fake" nutrients added to wheat flour.  The niacinamide, folic acid and so on that you see on the ingredients list of that bread at the grocer's are all "fake" vitamins.   They are not the same chemical form as those in unprocessed food and will cause similar symptoms to celiac in people with genetics that can't handle them.