Do i need a colonoscopy to detect crohns?

Usually the: Doctor may suspect crohn's but a colonosocpy can help with the extent of the disease and also confirm with biopsies of the terminal ileum/small bowel and the colon.

Yes: A complete screening colonoscopy with multiple biopsies is required to accurately diagnose crohn's disease, and assess the current status of this chronic inflammatory bowel disease.

See below: There are other ways it can be detected such as cat scan, however, colonoscopy is often done because a biopsy to confirm the diagnosis can be done during the procedure.