@Chrissysoul, your doc is right. there is not 100% guarntee one way or other. Not even biopsy. Granulomas are found only in 20-30% of people with crohns. I have indermined colitis that means they can not tell uc or crohns. My GI wants to see how it develops over time. He had one patient who had surgery 25 years ago now has been diagnosed with crohns.
There are different types of crohns based on disease location and pattern. Based on disease locations Gastroduodenal Crohn's Disease, Jejunoileitis,Ileitis,Ileocolitis and Crohn's Colitis.
Based on pattern it could be Inflammatory,Fibrostenotic or Fistulizing.
So if some one have crohns colitis and inflammatory type, it is almost like UC. But if some one have UC and ends up with fistula or narrowing than most probably it is crohns.