I had a bout of myocarditis a few years back. Being in many ways indistinguishable from a heart attack, it prompted the ER folks to perform an angiogram. They shaved me completely "down there" and went in via the femoral artery. Thinking back, I don't remember their having much concern about cleanliness, though I'm not IC and didn't express that particular concern to them either. Instead, the concern was for blood clots at the catheterization site. I was to feel it regularly, and was told to call 911 immediately if I felt a lump larger than a pea.
If you're dealing with urinary IC only, I don't know that you should worry too much, but as acorn suggests, the best bet is to talk with the doctors.
As for the procedure itself: I was initially terrified, believing as the doctors did that I was having a heart attack and was likely to die if not for their immediate intervention. Shortly before being wheeled into the OR, a nurse who had just finished installing IVs in both of my arms told me that she was giving me something that would make me--her words--"not worry".
What followed was an interesting, almost out-of-body experience. I can remember feeling very cold as I lay on the table, watching the whole process. The catheterization itself was relatively painless. The monitor was right next to where I was lying, and I got to see the live video of my own heart beating and the dye spreading, illuminating (in a sense) all of the tiny blood vessels. I guess I would describe it as having all of my senses switched to "record", but being unable to really process any of it until later. It was odd, and certainly an interesting experience. Of course, the circumstances weren't anything enviable.
In the end, no blockages were found, and the diagnosis was inflammation. I was given mega-doses of NSAIDs and discharged the next day. And I didn't die! WOOT!
Take care. I expect all will go well.