When should I start screening colonoscopy?

Screening means testing a person who has no symptoms, so that polyps or early cancer are found if present. A common question from patients is: “From what age?”. There is no single answer, because different guidelines give different numbers and each person’s risk differs.

Why does screening matter?

ASCRS says almost all colon cancers start from polyps and polyps can be removed at colonoscopy, so the test is both diagnosis and prevention. Many colon cancers have no symptoms at first. NCI also writes that new cases in adults under 50 rose by about 2.4% a year between 2012 and 2021 (this figure comes from US statistics and may not be exactly the same for our country).

From what age? Guidelines differ

• ASCRS (the American Society of Colon and Rectal Surgeons) recommends starting at age 45 for a person at average risk and regards regular screening from 45 to 75 as appropriate. This change was made in 2018 based on the rise in cancer under age 50.
• The NHS (England) has its national program from age 50 to 74, every two years, with a home stool test kit (FIT). People aged 75 and over can request one.
• Guidelines in other countries and organizations may give other numbers. The national program and insurance in your country may also differ.

So the “right age” depends on the guideline your doctor trusts and your personal risk. Talk to your doctor.

Family history changes everything

ASCRS says:

• If someone in the family has had bowel cancer or polyps, start at age 40 or 10 years before the age at diagnosis of the youngest affected relative (the text gives both without preferring one). For example, if your father was diagnosed at 48, start at 38.
• Lynch syndrome (an inherited type): colonoscopy every 1 to 2 years from age 20 to 25.
• Familial adenomatous polyposis (FAP): annual sigmoidoscopy from puberty if genetic testing is positive or uncertain.
• Inflammatory bowel disease (colitis and Crohn’s colitis): risk is higher. ASCRS says the risk depends on the extent, duration and severity of inflammation, and after 8 years or more a colonoscopy with biopsies every 1 to 2 years is advised. For Crohn’s disease, ASCRS says the first colonoscopy should be within the first 8 years from the start of symptoms.

If you have symptoms yourself (blood in the stool, a change in bowel habit, anemia, weight loss), this is not about screening; you need to be assessed.

The tests

ASCRS and NCI list these options:

• Colonoscopy: the whole large bowel is seen and a polyp can be removed at that moment. If the result is normal, ASCRS gives an interval of 10 years (in a person at average risk and with no new symptoms). ASCRS regards colonoscopy as the preferred first test.
• Fecal occult blood test (FOBT/FIT): yearly (ASCRS); the NHS every two years with FIT. Better at finding cancer than polyps; an abnormal result must be followed with a colonoscopy.
• Sigmoidoscopy: every 5 years, sees only the lower part of the bowel.
• CT colonography or barium enema: ASCRS mentions every 5 years for people who cannot tolerate colonoscopy or whose colonoscopy was incomplete. On one ASCRS page CT colonography is not recommended for routine screening. See what your doctor says.
• Stool DNA test: on this page ASCRS does not currently recommend it for routine screening, while NCI counts it among the available tests. The difference between the texts shows that this area is changing.
• Blood test: ASCRS says it is not yet accurate enough for screening.

NCI reminds us that any test may give a false negative or positive result and colonoscopy has rare complications such as a tear and bleeding. NIDDK gives, in one screening study, a hole in the bowel at about 3 per 10,000 and bleeding at about 15 per 10,000.

After a polyp is removed

ASCRS gives the general follow-up schedule like this (depending on number and size):

• 1 to 2 small polyps under 1 centimeter: repeat after 5 years
• 3 to 4 small polyps or one polyp larger than 1 centimeter: 3 years
• 5 or more small polyps, or 3 or more large polyps: 1 year
• If a polyp was not removed completely: 3 to 6 months

On the polyp page, ASCRS says at least 30% of patients develop new polyps after removal, and follow-up is usually 3 to 5 years later. These two sets differ slightly and show that the doctor sets the schedule according to your findings.

What is a colonoscopy like?

The NHS and ASCRS say you take a laxative to empty the bowel, you usually get sedation, the test takes less than an hour and complications occur in fewer than 1%. Bowel preparation is the hardest part and our guide explains it. The NHS says it may be uncomfortable but should not be painful.

Summary

• The starting age differs between guidelines: 45 (ASCRS) or 50 (the NHS program).
• A family history, earlier polyps or inflammatory bowel disease bring the start earlier.
• Having symptoms means assessment, not screening.
• Talk to your doctor about the choice of test and the age.

This article does not replace a doctor’s opinion; ask your doctor about your own situation.