Transverse colon = the part that crosses your torso (under the navel) then joins the (left) descending colon near the spleen. "75% of colon now affected by UC" sounds about
right. If your right colon were affected, too, you'd have "pancolitis". "Sub-total" means less than total (colon area). Sorry that you have more inflammation than before; it's not uncommon with UC & your doctor is responding in the usual way, wanting to change your med(s) because what you've been taking does not seem sufficient to control the level of inflammation you have. / Old Hat (30 yrs with left-sided UC ... [etc.])