The American Cancer Society added blood testing to its colorectal cancer screening guideline on Wednesday, giving adults 45 and older a new option if they have not completed or have declined visual exams and stool tests. The recommended blood-based test is Shield, made by Guardant Health and approved by the US Food and Drug Administration in 2024.

The update matters because colorectal cancer is often caught too late, even though more than 90% of people diagnosed at stages I and II will survive at least five years. Almost all cases begin as precancerous polyps in the colon or rectum, which is why screening can change the outcome before cancer spreads.

Dr. William Dahut said the change fits patients who avoid the standard tests, noting that many people cannot or will not do a colonoscopy, or will not collect their own stool for testing. He said he believes it is the right option for the right population of patients, and that having more choices should help more people get screened early enough to be cured.

Even so, the new blood tests are not a full substitute for the tests doctors already trust most. Colonoscopies remain the gold standard, and blood-based screening is still recommended only for people who decline or do not complete preferred screening tests. The guideline also keeps visual exams and stool-based tests in place, including Cologuard Plus, an upgraded version of Cologuard, and ColoSense, a new FDA-approved test developed by Geneoscopy.

The friction is that blood tests are easier for some patients, but they are not as sensitive as other options at finding precancerous polyps. That tradeoff is central to the new recommendation, especially as colorectal cancer cases have risen at younger ages and doctors are trying to keep people from skipping screening altogether. The new guideline opens another door, but it does not erase the fact that the most effective tests are still the ones many people avoid.

What happens next is straightforward: doctors and health systems will have to decide how quickly to fold the new recommendation into routine care. For patients who have already put off screening, the update gives them one more way to start now instead of waiting for a test they are more comfortable avoiding.