Hello My Husband Has Had Some Rectal Bleeding And Stomach

Hello
My husband has had some rectal bleeding and stomach pain on his left side. A couple of days later he made an appt. w/his primary & was told to go the emergency room, where he had a CT scan & some blood work. he was than told it was colitis, was discharged and to follow with a Gastro dr. he had his appt. with the gastro today and was told he needed an endoscopy, set for next Tuesday. shouldn't he have a colonoscopy first, to rule out Diverticulitis???? is this correct.
his wife linda