Colonoscopy and flexible sigmoidoscopy

These are descriptions of two procedures on public pages opened October 30, 2026. ahem does not perform them. The shorter office scopes used when hemorrhoids are one question, including an anoscope, are on what a hemorrhoid exam checks.

NIDDK's colonoscopy page says a doctor uses a flexible tube with a camera to look inside the rectum and colon, which make up most of the large intestine. It can show irritated and swollen tissue, ulcers, polyps, and cancer. Reasons it lists include bleeding from the anus, changes in bowel movements such as diarrhea, pain in the abdomen, and unexplained weight loss. Doctors also use it to screen for colorectal cancer when a person has no symptoms.

NIDDK's flexible sigmoidoscopy page says the scope looks inside the rectum and lower colon. The overview says the lower colon includes the sigmoid colon and descending colon. The procedure section says the doctor slowly removes the scope once it reaches the transverse colon. Both sentences are on that page. The same symptom list appears: bleeding from the anus, a change in bowel movements, belly pain, and unexplained weight loss. If the doctor finds abnormal tissue or polyps, NIDDK says a colonoscopy may be recommended to examine the rest of the colon.

Mayo Clinic dates its colonoscopy page February 6, 2026. It says a colonoscopy examines the inside of the colon, the rectum, and, when indicated, the end of the small intestine. It can investigate bleeding from the anus, changes in bowel movements, or belly pain, and it names colorectal cancer, inflammatory bowel disease, and diverticular disease among conditions it can help detect. In the comparison section, Mayo Clinic says a sigmoidoscopy examines only the lower part of the colon and rectum, and a colonoscopy examines the entire colon. Findings during sigmoidoscopy may require a colonoscopy afterward. Mayo Clinic does not print the 10-to-20-minute time.

NIDDK says a colonoscopy usually takes less than one hour, and that a health professional gives sedatives, anesthesia, or pain medicine through a vein so the person is not aware or does not feel pain. Afterward the person stays about 30 to 60 minutes while those medicines wear off, and should expect a full recovery and a return to a normal diet by the next day. Cramping or bloating can occur in the first hour. A ride home is required because driving is not safe until the medicines wear off.

Mayo Clinic says a colonoscopy typically takes about 30 to 60 minutes, and that sedation or anesthesia through a vein is usual. The team monitors the person for about an hour afterward. It says most people return to their usual activity by the next day, and that someone needs to take the person home. It also says not to drive, return to work, or make important decisions for the rest of the day. NIDDK's less-than-one-hour line and Mayo Clinic's about-30-to-60-minutes line both describe the procedure. They were not collapsed into a third number. The recovery stay is about 30 to 60 minutes on NIDDK's page and about an hour on Mayo Clinic's.

Flexible sigmoidoscopy, on NIDDK's page opened October 30, 2026, usually takes about 10 to 20 minutes. A person typically does not need sedatives or anesthesia. The procedure can be done at an office visit, a hospital, or an outpatient center. Pressure or cramping can occur while the colon is inflated with air. If no sedative was given, NIDDK says a person can typically return to a normal diet and activities right away. That 10-to-20-minute figure is NIDDK's.

NIDDK says colonoscopy prep includes a special diet for a few days, a bowel cleaning, and a ride home. Foods with a lot of fiber, such as whole grains, raw vegetables, beans, and nuts and seeds, may need to be avoided for several days. A clear-liquid diet may last a day or more. The page says a doctor may recommend avoiding red- and purple-colored drinks or gelatin. Bowel prep often means drinking a large amount of liquid laxative, most often the night before and the morning of the procedure, and it causes diarrhea. NIDDK says the prep should be finished even though that part is difficult.

Mayo Clinic says preparation usually begins 1 to 2 days before the procedure. A low-fiber or low-residue diet may come first. The day before, solid food typically stops and a clear liquid diet starts. It says not to drink red liquids because they can be mistaken for blood. Bowel prep often starts the evening before, and some regimens use a dose that night and another the morning of the exam. Stool typically changes from solid to loose and then to watery and light colored or clear. Mayo Clinic says to finish the prep even if the stool looks clear before the last dose.

NIDDK says flexible sigmoidoscopy often requires less bowel prep than colonoscopy. It may still include enemas or laxatives, and it may include avoiding dairy and high-fiber foods for several days plus a clear-liquid diet. The written instructions from the clinician are the schedule. These pages do not replace that sheet.

NIDDK's colonoscopy page says a doctor will recommend colorectal cancer screening starting at age 45 for someone without health problems or risk factors that raise the chance of colorectal cancer. If a person is older than 75, NIDDK says to talk with a doctor about whether screening should continue. The flexible sigmoidoscopy page also uses age 45 for that average-risk start, and it says doctors may recommend colonoscopy for screening because it shows the entire colon, while a flexible sigmoidoscopy may take less time and may not need sedation.

Mayo Clinic says that for people at average risk, colorectal cancer screening is recommended to start at age 45. Colonoscopy is one option. It may be repeated every 10 years when findings do not require earlier follow-up. Mayo Clinic also says another colonoscopy in 7 to 10 years may be advised if only one or two small polyps with low-risk features were removed, and in 1 to 5 years for some higher-risk findings. The 10-year, 7-to-10-year, and 1-to-5-year lines are Mayo Clinic's, dated February 6, 2026 and opened October 30, 2026. NIDDK's colonoscopy page does not print those intervals. Why a polyp can bleed in a way that resembles other problems is on a colon polyp and rectal bleeding.

NIDDK says the risks of colonoscopy include bleeding, perforation of the colon, a reaction to the sedative, and severe abdominal pain. A study of screening colonoscopies, cited on the page last reviewed in August 2023, found perforation in about 3 out of every 10,000 procedures and bleeding in about 15 out of every 10,000. Most of those cases were in people who are older or who had polyps removed. Delayed bleeding can occur up to 2 weeks later. Light bleeding from the anus after a polyp removal or a biopsy is described as normal.

For screening flexible sigmoidoscopy, NIDDK cites a study that found perforation in about 1 out of every 50,000 procedures and bleeding in about 1 out of every 20,000. Most bleeding cases were in people who had polyps removed. Delayed bleeding can occur several days later. The 3-in-10,000 and 15-in-10,000 figures belong to colonoscopy. The 1-in-50,000 and 1-in-20,000 figures belong to flexible sigmoidoscopy. They were not averaged.

Mayo Clinic's risk list is bleeding, most often after a polyp or a tissue sample is removed; a tear in the colon wall, which may need further treatment or surgery; and reactions to sedation, including breathing or heart problems, particularly in older adults or people with other medical conditions. Mayo Clinic does not print the per-10,000 counts.