EDIT: in the absence of antibodies the biopsy would still show:
-Crypt hyperplasia with a decreased villi/crypt ration. Crypts are grooves between the villi, which are the small fingerlike projections that line the small intestine and promote nutrient absorption. Crypt hyperplasia is when the grooves are elongated compared to a normal intestinal lining which has short crypts.
-Blunted or atrophic villi. This is a shrinking and flattening of the villi due to repeated gluten exposure.
https://celiac.org/about-celiac-disease/screening-and-diagno...
Because getting the test would require about a month of agonizing pain with constant diarrhea, perhaps? Just to get a formal confirmation of something they're already pretty sure of.
The genetic test can rule in / rule out - and when combined with your history would be called a diagnosis by many physicians. I was in your same situation and couldn’t contemplate eating gluten again after understanding life without it.
Random tip: if you accidentally expose yourself to gluten, taking Benadryl right away can help with the flu-y sort of inflammatory symptoms. You’ll still get the gastric distress, but you might not feel like you have the flu for the next week, which for me is the worst part.