What diseases can't be spotted via a colonoscopy?

Colonoscopy is effective for detecting many conditions, but it may not identify certain diseases such as small bowel disorders, inflammatory bowel disease (IBD) in its early stages, or microscopic colitis, as these conditions often affect areas not reached by the scope. Additionally, some cancers, like those in the rectum or distal colon, may be missed if they are located in hard-to-reach areas or are very small. Conditions like diverticulitis may also not be clearly visible during the procedure. Lastly, certain functional disorders, such as irritable bowel syndrome (IBS), do not show up on colonoscopy.