Colon Cancer Screening: When to Start and How to Choose a Test

If you're 45 and feeling fine, colon cancer screening probably isn't on your radar yet. It should be. National guidelines moved the recommended starting age down from 50 to 45 a few years ago, and the reason is straightforward: more adults under 50 are being diagnosed with colorectal cancer than in the past. The good news is that you have real options for how to screen, and none of them require you to feel sick first.

Why the starting age is 45, not 50

For decades, 50 was the standard age to begin colorectal cancer screening. In 2021, the US Preventive Services Task Force lowered that to 45 for adults at average risk, based on evidence that colorectal cancer rates in people in their 40s had climbed substantially and that an estimated 1 in 10 new cases were occurring in people younger than 50 (https://doi.org/10.1001/jama.2021.6238). More recent modeling suggests this trend has continued, with early-onset colorectal cancer incidence in the United States rising by nearly half over the past three decades, a shift researchers link to diet, body weight, and other factors that build up over years, not a single cause (https://doi.org/10.21037/jgo-2026-0314).

Colorectal cancer is still uncommon before 45, and most people who develop it are older. But screening exists precisely because this cancer usually starts as a slow-growing polyp that can be found, and often removed, years before it would ever cause a symptom. That lag is what makes screening worth doing before anything feels wrong.

What each screening test actually involves

There isn't one right test. There are several accepted options, and the right one depends on your health history, your tolerance for prep and downtime, and how consistently you're likely to repeat it.

Colonoscopy. A gastroenterologist examines the entire colon with a camera while you're sedated, after a bowel prep the day before. If a polyp is found, it's typically removed during the same procedure, which is why colonoscopy is both a screening and a treatment tool in one visit. At average risk, it's repeated every 10 years.

Fecal immunochemical test (FIT). An at-home test that checks a small stool sample for hidden blood, done once a year. It's simple and requires no prep or sedation, but it only screens, it doesn't remove anything, and it needs to be repeated annually to stay effective.

Stool DNA test (FIT-DNA). Also done at home, this test checks stool for both blood and DNA changes associated with polyps and cancer, repeated every one to three years. One study evaluating this test specifically in 45- to 49-year-olds found it correctly ruled out advanced polyps and cancer about 95% of the time in people without those findings (https://doi.org/10.1158/1940-6207.CAPR-20-0294). It's more sensitive than FIT alone but also produces more false positives, which can mean an unnecessary follow-up colonoscopy.

CT colonography and flexible sigmoidoscopy are used less often but remain options in specific situations. Your clinician can talk through whether either makes sense for you.

Colonoscopy versus stool-based testing: how to choose

This is less about which test is "best" and more about which one you'll actually complete, since the least effective test is the one that doesn't get done.

A large randomized trial that followed over 53,000 adults compared one-time colonoscopy against FIT repeated every two years. Notably, more people actually completed FIT screening than showed up for their scheduled colonoscopy (34% versus 25%), and the two approaches found colorectal cancer at similar rates on that first round. Colonoscopy did detect more precancerous polyps, since it looks at and treats the whole colon directly rather than relying on a blood signal in stool (https://doi.org/10.1056/NEJMoa1108895).

In practical terms: colonoscopy is more thorough and handles prevention and detection in a single visit, but it means a day of prep, sedation, and someone to drive you home, and it's typically the higher-cost option out of pocket if not fully covered. Stool-based tests are far more convenient and have no prep, but they have to be repeated on schedule, and a positive result still means a colonoscopy is needed to find the source. Neither choice is a compromise. The test you'll actually keep up with is the one doing you the most good.

When you should start earlier than 45

Average-risk guidelines don't apply to everyone. You may need to start screening earlier, or screen more frequently, if you have:

• A first-degree relative (parent, sibling, or child) who had colorectal cancer or an advanced polyp, especially if they were diagnosed before 60
• A personal history of inflammatory bowel disease, such as Crohn's disease or ulcerative colitis
• A known hereditary condition such as Lynch syndrome or familial adenomatous polyposis
• Rectal bleeding, a persistent change in bowel habits, unexplained abdominal pain, or unintended weight loss, at any age. These symptoms warrant an evaluation on their own, not a wait for your next scheduled screening.

If any of these apply to you, screening decisions are individualized, and that conversation is worth having directly with a clinician rather than defaulting to the standard timeline.

What a positive stool test actually means

A positive FIT or stool DNA result is not a cancer diagnosis. It means blood or abnormal DNA was detected, and the next step is a colonoscopy to find out why. Most of the time, the cause turns out to be a polyp, hemorrhoids, or something else benign. But that follow-up colonoscopy isn't optional; it's the part of the process that actually confirms what's going on, and skipping it defeats the purpose of having screened at all.

Getting screening started

Colon cancer screening is one of the few cancer screenings where catching something early can mean removing it before it's ever cancer. Figuring out which test fits your history, your risk factors, and your life is exactly the kind of conversation a primary care visit is for. Stonewood Health's telehealth primary care team can review your personal and family history, order the right stool-based test, or refer you for a colonoscopy with a local endoscopy provider, all without you needing to set foot anywhere in person. Most major plans are accepted, including Medicare. Visit /conditions/primary-care to get started.