Colorectal cancer is one of the few cancers that screening can prevent outright. Most cases start as a polyp that grows slowly over years, and finding polyps early enough to remove them interrupts the disease before it becomes cancer at all. That is a rare and valuable feature of a screening test.
In 2021 the U.S. Preventive Services Task Force lowered the starting age for average-risk screening from 50 to 45. The change reflected a steady rise in colorectal cancer among younger adults that has not been fully explained. If you are in your mid-forties and no one has raised this with you, it is worth raising yourself.
Who counts as average risk, and who does not
Average-risk screening starts at 45 and continues through age 75, with individualized decisions between 76 and 85. Higher-risk categories need earlier and more frequent screening, and it is common for people to underestimate which group they belong to.
Higher risk includes:
- A first-degree relative with colorectal cancer or advanced adenomas, particularly if diagnosed before age 60.
- A personal history of inflammatory bowel disease, especially longstanding ulcerative colitis or Crohn colitis.
- A known or suspected hereditary syndrome such as Lynch syndrome or familial adenomatous polyposis.
- A prior finding of adenomatous polyps on a previous colonoscopy.
Any of these usually shifts the starting age earlier and the interval shorter. If you have a parent or sibling with colorectal cancer, share the age of their diagnosis with your clinician; it directly changes when you should begin.
The tests, honestly compared
Several tests are endorsed, and the best test is the one you will actually complete.
- Colonoscopy every 10 years remains the reference standard. It examines the entire colon and permits polyp removal in the same session.
- FIT (fecal immunochemical test) every year is a stool test that looks for occult blood. It is inexpensive, involves no bowel prep, and reduces mortality in randomized trials.
- Multi-target stool DNA tests (such as Cologuard) every one to three years combine DNA markers with FIT. Sensitivity is higher than FIT for cancers and advanced polyps but false positives are more common.
- Flexible sigmoidoscopy every 5 to 10 years, sometimes paired with annual FIT, is used less often in the U.S. but is supported by strong trial evidence.
- CT colonography every 5 years is an option where available.
Any positive non-colonoscopy test should be followed by a diagnostic colonoscopy. A positive stool test is not a diagnosis; it is an indication for the definitive exam.
The worst screening strategy is an excellent test that sits in a drawer. A completed FIT beats a colonoscopy you keep postponing.
Symptoms that override screening
Screening tests assume you are without symptoms. Any of the following deserves prompt evaluation regardless of your last screen:
- Rectal bleeding or blood in the stool
- A persistent change in bowel habits
- Unexplained iron-deficiency anemia
- Unintentional weight loss
- New, unexplained abdominal pain
These warrant a diagnostic workup, not a routine screening test.
Prep, sedation, and other frictions
Most complaints about colonoscopy concern the preparation rather than the procedure. Split-dose regimens, in which half the prep is taken the morning of the exam, are more effective and better tolerated than single-evening dosing. Ask specifically for a split-dose plan.
Sedation practices vary, and it is worth asking whether your center uses moderate sedation or propofol; either is reasonable. Serious complications are uncommon but not zero, and any center should be able to quote its own perforation and bleeding rates on request.
The bottom line
Colorectal cancer screening is one of the strongest cases in preventive medicine: a common, deadly disease with tests that prevent it. If you are 45 or older, pick a test you will actually finish. If you have a family history, start the conversation earlier and be specific about ages of diagnosis.