The gold standard for celiac testing is an intestinal biopsy with at least a half dozen villious samples taken from various locations. But one can get a celiac serologic panel done to see if anything shows up there. This consists of measurements of anti-gliadin IgG (the most sensitive but least specific indicator of gluten problems), anti-gliadin IgA, anti-tranglutaminase IgA (the most specifically associated with villious damage) and total IgA (because congentially low levels of this can skew the other tests).

I don't think that 5.2 A1C level is bad at all (I wish mine was that low). But if you do want to get a glucose tolerance test done I'd recommend a five hour one with draws for both insulin AND glucose done at half-hour intervals. You want to see what your starting insulin levels are--to see if you have a degree of insulin resistance--and then see the patterns of insulin and glucose rise and fall. Often pre-diabetics need to overproduce insulin during glucose challenge to keep the blood sugar levels in check.

As for the skin biopsy numbers, if you are developing a length dependent neuropathy, in which the nerve endings farthest from the center of metabolic processes are affected first and "die-back", you would have lower numbers from the ankle and foot area than from the thigh. Of course, the problem here is that you haven't met the fifth percentile cut off criteria for definitive diagnosis of small fiber neuropathy that, in my opinion, was rather arbitrarily set when the original norming was done at Johns Hopkins a few decades ago (see "McArthur protocols"--you can also search my name on this board as I've written a lot about this). We don't know, of course, what your numbers would have been if you'd had a skin biopsy before symptoms started--e.g., what your "normal" was--and if the current numbers represent a significant decrease from that. Fortunately skin biopsy is repeatable and another one a year from now, if symptoms persist, may uncover trend lines.

Given where you went (Cornell) I imagine they titred you up for a lot of the antibodies to peripheral nerve (and probably did the celiac panel too), but just is case, check you testing against this (since it was written by Latov anyway):

https://www.questdiagnostics.com/tes...ripheralNeurop