Colorectal cancer screening: at what age and with which test?

What does screening mean?

Screening means checking people who have no symptoms, in the hope of finding a problem before symptoms appear. In the colon this can even find a polyp before it turns into cancer. This is different from “checking for symptoms.” If you have seen blood in your stool or your toilet habits have changed for months, you are seeing a doctor because of symptoms and this is not about screening; you need to be examined and should not wait until a certain age. See these in urgent warning signs.

Starting age: the guidelines do not speak with one voice

Read this section carefully, because when someone says “the screening age is such-and-such,” it is not always the full picture.

• USPSTF (United States): recommends screening from age 45 to 75. Grade A for ages 50 to 75 and grade B for ages 45 to 49 (a weaker recommendation than A, but still a recommendation). For ages 76 to 85 the decision is made case by case. For age 86 and over, evidence is lacking and a benefit is unlikely.
• American Cancer Society: from age 45 for people at average risk. Up to 75 for older adults with a life expectancy of more than ten years; 76 to 85 based on the person’s condition and preference; and stopping after 85.
• ACG (American College of Gastroenterology, 2021): “recommends” screening for ages 50 to 75 but only “suggests” it for ages 45 to 49, which is a milder position.
• WHO: does not give a specific starting age in its fact sheet. It says the disease mostly affects people over 50 and that risk rises noticeably after this age, and that in some places the burden of disease is also rising at ages 30 to 50. It considers screening the most effective way of detection when an organized program exists.
• National program in England (NHS): from age 50 to 74, sends a home stool test kit every two years.

So “45” and “50” both appear in reputable guidelines. The reason is differences in the circumstances of countries and in the strength of evidence for ages 45 to 49. What age is right for you depends on your personal risk, and your doctor decides it. These guidelines were written for other countries, and for Iran the doctor needs to decide.

What does average risk mean?

The American Cancer Society defines average risk this way: no personal history of colorectal cancer or certain polyps, no family history of colorectal cancer, no inflammatory bowel disease (Crohn’s or colitis), no hereditary syndromes such as Lynch syndrome and polyposis, and no earlier radiation treatment to the abdomen and pelvis. If you have any of these, the list above is not for you.

Family history brings the starting time forward

The American Cancer Society says people at higher risk may be checked earlier or more often, and the starting time depends on which relative was affected and at what age. For someone who has a first-degree relative (parent, sibling or child) with cancer or an advanced polyp before age 60, or who has two affected first-degree relatives, the ACG patient summary suggests starting colonoscopy at age 40 or ten years before the age of the youngest affected relative, whichever is earlier. The doctor sets the exact details based on the full guideline. People with inflammatory bowel disease and hereditary syndromes also have a separate schedule. If your family has such a history, write down the age and relationship of the affected person and tell your doctor.

With which test?

USPSTF, the American Cancer Society and ACG emphasize common methods:

• A stool test at home, such as the fecal immunochemical test (FIT), which is usually done yearly and needs no bowel preparation.
• Colonoscopy, which is normally done once every ten years and needs bowel preparation. See the preparation guide.
• Other options such as sigmoidoscopy, CT colonography and stool DNA testing are included in some guidelines.

ACG says the best test is the one that is accepted and actually done. Any non-colonoscopy test that comes back positive must be followed by a colonoscopy. The NHS also says blood in a stool test is not necessarily cancer and has more common and simpler causes such as an anal fissure and polyps, but it must be clarified with a colonoscopy.

The choice of method is yours, together with your doctor. Some people prefer colonoscopy because the result and the treatment of polyps happen on the spot, and some prefer the home test for convenience.

Common worries

• “If I have no symptoms, I don’t need it.” Screening is exactly for people with no symptoms. WHO says the disease in its early stages often has no symptoms or only mild ones.
• “Colonoscopy is dangerous.” NIDDK says bleeding and perforation of the bowel are rare but possible. NIDDK cites a screening study in which perforation occurred in about 3 and bleeding in about 15 of every 10,000 colonoscopies. Talk with your doctor about your own risk.
• “What about after 75?” USPSTF and the American Cancer Society say that for ages 76 to 85 the decision should be case by case. For an older person whose child books the appointment, overall health and the history of earlier checks matter more than age.

Symptoms mean it is not screening

The NHS lists the main symptoms this way: a change in stool or toilet habits, blood in the stool or bleeding from the anus, abdominal pain or bloating, unexplained weight loss, tiredness. It says most people who have these do not have cancer, but they need to be checked. If you have any of them, whatever your age, make an appointment. You do not need to reach the “screening age.”

Summary

• Screening is for people without symptoms; symptoms mean seeing a doctor, not waiting.
• Guidelines differ on the starting age (45 or 50), and the right age for you depends on personal risk, so settle it with your doctor.
• If colorectal cancer or an advanced polyp has occurred in your family, tell your doctor the age and relationship of the person.
• A home test or a colonoscopy; whichever gets done is better than neither, and a positive home test means a colonoscopy.