Blood test for colorectal cancer (Shield)
Finds most cancers but few precancers; a fallback, not a first choice.
What studies found
In the ECLIPSE study, the Shield blood test detected 83% of colorectal cancers but only 13% of advanced precancerous lesions. The American Cancer Society's 2026 update recommends blood tests only for people who decline or don't complete the preferred stool tests or colonoscopy.
The catch
Because it finds few precancers, it prevents fewer cancers than stool tests or colonoscopy, and no study has shown it lowers deaths.
What to do
Choose a stool test or colonoscopy if you can. Use a blood test only if you won't do either.
Sources
Rung 2 of 5, Limited: Few, small or conflicting human studies, or only indirect measures such as blood markers. How we score
Step by step
For the whole picture, from prevention and screening to treatment and life after, see the colorectal cancer page.
Related
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