Angela, hi. It is possible that your drs. DID do certain blood tests for vasculitis & Celiac, but just didn't tell you? That probably happens more often than we realize, so the only way to know is to ask.
IBS: I think it's a "diagnosis of exclusion", meaning the diagnostician has to first rule out BIG things like the IBD's, Celiac, vasculitis, etc.
All the above are diseases (or conditions), but I think "Russell Viper Venom" is a TEST, used evaluating for Antiphospholipid Syndrome (APS), which you can read about in the "sticky post" section at the top of the thread list. (APS can cause clots & other things as well.) Also, I think certain results can hint at some rare inherited "factor deficiencies" (like Leiden or Factor X, neither of which I understand at all).
Well, gee... this is a ONE BIG PLATEFUL of thoughts, and some could be flat-out wrong! (Just being honest.
) But you're reading, forming questions, and looking back at your life history; and I think that's really important given your major bowel surgery and other issues. I hope you talk with your rheumatologist, to make sure your GI issues have given the attention they deserve, that YOU deserve. Like I said, all sorts of things may have been considered, but I'd want reassured that they were. And if not, then now's the time! Good talking with you. Keep us posted. We'll be thinking of you. All my best, Vee