What a colonoscopy can show

A colonoscopy lets your healthcare professional look directly at the inside of your colon and rectum to check for changes or signs of disease. The exam can reveal:

• Polyps. These are small growths on the lining of the colon that can be precancerous or noncancerous, also called benign. Most polyps are harmless. But removing polyps during colonoscopy helps prevent colorectal cancer.
• Cancer. A colonoscopy can find signs of cancer, such as areas on the colon lining that look uneven, swollen or have open sores.
• Inflammation. Areas of redness, swelling or sores may indicate irritation or an inflammatory condition, such as colitis. The appearance and location of inflammation can help determine whether it's due to infection, inflammatory bowel disease or another cause.
• Bleeding. The test can identify where bleeding is coming from inside the colon. Bleeding is often caused by ulcers, hemorrhoids, fragile blood vessels or areas of inflammation. Finding the source of bleeding helps doctors treat the problem and prevent further blood loss.
• Diverticulitis. A colonoscopy can show small pouches, called diverticula, that form in the wall of the colon. These pouches are common and usually harmless. If they become inflamed or infected, the condition is called diverticulitis. A colonoscopy is often done after recovery from diverticulitis to rule out other causes of symptoms.
• Hemorrhoids. The procedure can show swollen veins in the rectum or anus that may cause pain, itching or bleeding. These are common and often related to straining, constipation or pregnancy. Finding hemorrhoids during a colonoscopy helps rule out other potential causes of rectal bleeding.
• Parasites. In uncommon cases, a colonoscopy may incidentally reveal other issues, such as visible parasites. However, these findings are unusual. Stool tests are typically used to diagnose parasitic infections.

• Other signs of digestive disease. The exam may show changes that suggest inflammatory bowel diseases such as Crohn's disease or ulcerative colitis. Colonoscopy allows doctors to view inflammation directly and take small tissue samples, called biopsies, to confirm the diagnosis and guide treatment.

  If you have diarrhea, inform the healthcare professional who is doing the colonoscopy. The health professional may consider assessing for microscopic colitis. This condition causes a type of inflammation only seen from a biopsy, as the colon lining often appears healthy.

  A colonoscopy also can help rule out other causes of symptoms that overlap with irritable bowel syndrome (IBS) or celiac disease. However, these conditions are not diagnosed by colonoscopy.

If necessary, polyps or small pieces of tissue can be removed during the procedure. These samples are then examined in a laboratory to confirm or rule out certain conditions.