Both colonoscopies and sigmoidoscopies are outpatient procedures that use flexible lighted tubes with video cameras to examine a patient's rectum and colon. A doctor uses a colonoscopy to view the entire length of a colon, while a sigmoidoscopy, which employs a shorter tube, is limited to the lower colon, according to the American Cancer Society.
Colonoscopies are performed by gastroenterologists, doctors specializing in the digestive tract, or surgeons who are looking for signs of cancer. Sigmoidoscopies can be performed by general care practitioners and may be used for cancer screening and to evaluate abdominal pain or causes of rectal bleeding, explains WebMD.
Colonoscopies take longer, usually about 30 minutes, versus the 10 to 20 minutes for a sigmoidoscopy, and while both are outpatient procedures, colonoscopy patients are usually given medicine to relax or sleep. This can mean significant post-op wooziness, while sigmoidoscopy patients rarely need medicine and usually are able to walk out the door. Colonoscopies require a 24-hour bowel-cleansing regimen, which most patients consider the worst part of the procedure, but usually no advance preparation is needed for a sigmoidoscopy beyond on-site enemas. If there are no signs of cancer, doctors typically recommend a colonoscopy every 10 years for patients over 50 years old. Sigmoidoscopies are suggested every five years for those in that age group, notes the American Cancer Society.