Colorectal screening now starts at 45. Here is what the tests are and why the age dropped

Colorectal cancer is one of the few cancers that screening can prevent outright, not just catch early: most cases begin as a polyp that takes years to turn malignant, and removing the polyp removes the future cancer. That is why the guidance has two features worth understanding — a menu of tests that work in different ways, and a starting age that recently dropped from 50 to 45.

The two families of test

Screening options fall into two groups. Stool-based tests look for hidden blood or altered DNA shed by a cancer or large polyp; they are done at home, are non-invasive, and are repeated at short intervals. Structural, or visual, examinations — colonoscopy chief among them — look directly at the lining of the bowel and can remove polyps in the same session, but are invasive and require bowel preparation.

The American Cancer Society frames the choice plainly: adults at average risk should have regular screening with either a high-sensitivity stool-based test or a structural examination, depending on patient preference and test availability [s2]. The crucial rule ties the two together — any positive result on a non-colonoscopy test must be followed by a timely colonoscopy, or the screening is incomplete [s2]. Screening with any one of the recommended options reduces both colorectal cancer incidence, by finding and removing precancerous polyps, and deaths [s2]. There is no single best test; the best test is broadly the one a person will actually complete.

Why the starting age fell to 45

For years, average-risk screening began at 50. It now begins at 45. The American Cancer Society moved first, in 2018, when its modelling found that strategies starting at 45 were efficient given changes in US colorectal cancer incidence [s2]. The US Preventive Services Task Force followed in 2021, extending its recommendation down to 45 [s1].

The Task Force graded the two age bands differently, and the distinction matters. Screening adults aged 50 to 75 is an A recommendation, reflecting substantial net benefit; screening adults aged 45 to 49 is a B recommendation, reflecting moderate net benefit [s1]. For adults aged 76 to 85 who have been screened before, it is a C recommendation — clinicians should offer it selectively, weighing overall health, prior screening and preference, because the net benefit across everyone in that band is small [s1]. All of this applies to people at average risk, meaning no personal history of colorectal cancer or adenomatous polyps, no inflammatory bowel disease, and no family history of a high-risk genetic syndrome such as Lynch syndrome or familial adenomatous polyposis [s1].

The reason behind the change: earlier disease

The age was lowered because the disease is shifting younger. The Task Force noted that an estimated 10.5 percent of new colorectal cancer cases now occur in people under 50, and that incidence among adults aged 40 to 49 rose by almost 15 percent from 2000-2002 to 2014-2016 [s1]. The American Cancer Society's later data show the trend continuing: colorectal cancer incidence in adults younger than 55 has been rising by 1 to 2 percent a year, and the cancer, which was the fourth-leading cause of cancer death in people under 50 in the late 1990s, is now first in men and second in women in that age group [s3]. The causes of the rise are not fully understood, which is itself an active area of research.

Uptake remains a weak point. As of 2016, 26 percent of eligible US adults had never been screened for colorectal cancer, and in 2018, 31 percent were not up to date [s1] — a large share of the potential benefit going unclaimed.

What this means for a reader

Colorectal screening is recommended from age 45 for people at average risk, and more than one test qualifies [s1][s2]. The choice between a home stool test and a colonoscopy involves real trade-offs — convenience and frequency against a one-time look that can remove polyps — and depends on individual risk, preference and what a health system offers; it is a decision to make with a clinician. Two things fall outside routine screening timing: a family history of colorectal cancer or a hereditary syndrome puts a person in a higher-risk category with different rules, and symptoms such as rectal bleeding, a persistent change in bowel habit or unexplained weight loss warrant medical assessment at any age rather than waiting for a scheduled screen.

Sources

• [s1] Screening for Colorectal Cancer: USPSTF Recommendation Statement, JAMA, 2021-05-18
• [s2] Colorectal cancer screening for average-risk adults: 2018 ACS guideline update, CA: A Cancer Journal for Clinicians, 2018-05-30
• [s3] Cancer statistics, 2024, CA: A Cancer Journal for Clinicians, 2024-01-17