Colonoscopy

Reasons you may not be able to have the test or why the results may not be helpful include:

• Having a barium enema within a week before the test. Barium can block your doctor's view of the colon.
• Having stool (feces) in the colon, a colon that has many turns, past surgery on the colon, or a lot of pain during the test.
• Taking iron supplements. This may make your stool turn black and make it hard to clean out the colon. Do not take iron supplements for several days before a colonoscopy.
• Drinking red or purple fluids, such as grape juice or fruit punch.
• Eating red or purple foods, such as grape Popsicles or cherry Jell-O.