Colitis can be caused by bacteria or other irritants, whereas ulcerative colitis is more specific. For example, my husband was hospitalized for nonspecific colitis, given IV antibiotics for 24 hours, sent home to finish up meds by mouth, and has never had another incidence. It was assumed to be bacterial due to the pattern of inflammation seen in xray. On colonoscopy done 2 months later, everything was still clear with no scarring or other.
Your doctor will be able to better determine if your colitis is UC based on biopsies taken during the colonoscopy. To state "undetermined" at this point is a safeguard because they probably could not rule out UC or Crohn's colitis by visualization alone. This is not uncommon to see on a colonoscopy report when the patient goes in with symptoms that go along with some form of inflammatory disease and the visual test is suspicious but not clear cut of what is going on. Your doctor is doing a good thing so far.
