Colorectal

Colorectal screening tests explained, and how to prepare

Colorectal cancer usually develops from the cells lining the colon and rectum. Years before turning into cancer, a small group of these cells grows into a polyp. Polyps usually cause no symptoms, but they often bleed and are easy to see during a colonoscopy. This is why screening works so well for colorectal cancer: polyps can be found, and removed, long before they become cancer.

Colonoscopy: the most complete test

A colonoscopy uses a thin, flexible tube with a camera (an endoscope) to look at the inside of the whole colon. It is done by a specialist, usually under sedation. The day before, you take laxatives so the bowel is empty and clean.

The main advantage is that, if a polyp or a suspicious area is found, a sample can be taken during the test, and small polyps can be removed straight away. If the colonoscopy is complete and normal, the next screening is due in 10 years.

A flexible sigmoidoscopy is similar but looks only at the lower part of the colon. It is repeated every 5 years, or every 10 years together with a yearly stool test.

Stool tests

Stool tests look for signs of cancer or polyps in a sample you collect at home. They are less invasive, but they need to be repeated more often, and any positive result means you need a colonoscopy.

• FIT (faecal immunochemical test) uses antibodies to look for hidden blood. A positive result doesn’t mean you have cancer, as bleeding has many causes, and a negative result doesn’t completely rule it out. It is repeated every year.
• Guaiac-based test (gFOBT) also looks for blood. For 3 days before, you may be asked to avoid red meat, vitamin C supplements and anti-inflammatory drugs such as ibuprofen. It is repeated every year.
• Stool DNA test with FIT looks for both blood and DNA changes shed by abnormal cells. You collect a whole bowel movement and send it to the lab. It is repeated every 1 to 3 years.

If you have seen blood in your stool or have other symptoms, a stool test is not the right test: see your physician.

CT colonography (virtual colonoscopy)

A CT scan creates images of the bowel without an endoscope. It needs the same bowel preparation with laxatives as a colonoscopy. It may be an option for people who can’t have a colonoscopy. It is repeated every 5 years, and an abnormal result needs a colonoscopy.

Colon capsule endoscopy

You swallow a capsule the size of a large tablet containing a tiny camera, which takes thousands of pictures as it travels through the gut. You change your diet for a few days beforehand and take laxatives. It is not among the tests the USPSTF currently recommends for screening.

This article gives general information and doesn’t replace advice from your physician. Want to know which screenings apply to you? Take the ScreenMe questionnaire.