Colorectal Cancer Screening: When to Start and Which Tests

What it involves

The National Cancer Institute explains that colorectal cancer starts in the colon or rectum, most often as an abnormal growth called a polyp on the inner lining. Most polyps do not become cancer, but a type called an adenoma is more likely to. Screening looks for these growths, or for cancer, in people who have no symptoms, and NCI says some tests let polyps be found and removed before they become cancer.

Who this is for

• Adults aged 45 or older who have never been screened or are not sure when they were last tested
• Patients with a family history of colorectal cancer or a personal history of advanced polyps
• Patients with inflammatory bowel disease such as ulcerative colitis or Crohn disease
• Patients who are due for a repeat test and want help choosing the next one

What to expect

• A review of your age, family history, personal history, and any past screening results
• A plain-language comparison of the test types, including stool tests and colonoscopy
• Help with next steps, including referral for tests done outside a primary care office
• A schedule for when your next test is due

Who should be screened and when

NCI says expert groups, including the US Preventive Services Task Force, generally recommend that people at average risk begin screening at regular intervals at age 45 and continue to age 75. For ages 76 to 85, the decision depends on life expectancy, health conditions, and prior screening results. People at increased risk because of a family history, advanced polyps, inflammatory bowel disease, or an inherited condition such as Lynch syndrome may be advised to start earlier or test more often.

The main test types

NCI describes several screening tests. These are the intervals it gives for each when it is the only test used at average risk:

• FIT or guaiac stool tests, which check for hidden blood, every year or two
• Multitarget stool DNA test, which checks blood plus DNA markers, at least every 3 years
• Colonoscopy, which examines the whole colon, every 10 years
• CT colonography, or virtual colonoscopy, every 5 years
• Flexible sigmoidoscopy, which examines the lower colon, every 5 or 10 years

Stool tests versus looking inside

NCI says stool tests are collected by the patient with a kit and sent to a lab, and that a positive result means a colonoscopy is advised. FIT usually needs no diet restrictions, while the older guaiac test does. Colonoscopy and the other direct viewing tests need the bowel cleared beforehand, and NCI says most colonoscopy patients receive sedation. A colonoscopy can remove growths during the test.

Risk factors beyond age

NCI lists age as a major risk factor, along with inherited conditions, a family history, and inflammatory bowel disease. Smaller increases in risk are linked to moderate to heavy alcohol use, obesity, physical inactivity, and cigarette smoking. NCI also reports that colorectal cancer is rising among younger adults and says the reason is not known. The obesity and BMI guide covers one of those factors. Belly pain that keeps returning is a separate question from screening, and the abdominal pain evaluation explains when pain needs urgent care and when it can wait for a visit.

If a test finds something

NCI says that if a stool test or any screening test other than colonoscopy finds an abnormality, a colonoscopy will be needed to look at the colon directly. During a standard colonoscopy, an abnormal growth is removed or biopsied and the cells are examined. Because a follow-up colonoscopy can be billed as a diagnostic exam, NCI advises checking with your insurer before the test about coverage and out-of-pocket costs. Diarrhea that lasts for weeks with no clear cause is evaluated separately from screening, as the persistent diarrhea guide explains.

Where screening fits in your yearly care

Screening is usually raised at preventive visits. The screenings by age guide puts it next to the other checkups, the Medicare wellness visit guide explains what that visit covers, and preventive care and chronic disease management describes how the practice follows long-term conditions. Screening is for people without symptoms; blood in the stool is a reason to book a regular visit now. A lasting change in bowel habits, such as new constipation, is worth mentioning at that visit, and the constipation guide lists the warning signs NIDDK says need a doctor soon. Rectal bleeding should not simply be assumed to be hemorrhoids, and the hemorrhoids guide explains why MedlinePlus says to have it checked.

Sources

• National Cancer Institute — Screening Tests to Detect Colorectal Cancer and Polyps