Is There a Blood Test for Colon Cancer?
Key takeaways:
There are two available blood tests for colon cancer. These tests can help screen for the condition, but they can’t confirm a diagnosis.
Blood tests aren’t recommended as a first-choice screening tool for cancer. A colonoscopy is still the best way to screen for and prevent colon cancer.
A blood test may be a good option for someone who’s not at high risk for colon cancer and who chooses to opt out of a colonoscopy.
Table of contents
Colorectal cancer is the fourth leading cause of cancer in the U.S. The best way to screen for colon cancer is with a colonoscopy. But this can be a barrier for many people to get the testing they need.
Blood-based tests are one of several screening options for colon cancer. They’re a newer way to screen for colon cancer. They may be more preferred than home-based stool tests because they don’t require you to collect your own stool sample.
But these tests aren’t the first recommendation for colon cancer screening. Here, we’ll cover why that is, as well as how they compare to other colon cancer screening measures.
How are blood tests used in screening for colon cancer?
There are a few different ways to screen for colon cancer, including blood tests. They look for specific substances in your blood that suggest cancer or precancer cells are present in your body. Blood tests don’t confirm a diagnosis.
It helps to know the difference between screening tests and diagnostic tests:
Screening tests look for a condition before symptoms start.
Diagnostic tests confirm what’s going on after symptoms have started.
Knowing your colon cancer risk: Having a family history of colon cancer, as well as a few other conditions, may increase your risk.
Understanding colon cancer trends: Why’s the rate of colon cancer actually increasing in adults under age 50?
Screening versus biomarkers: Some blood tests can look for colon cancer, whereas others can help experts tailor treatment plans.
Screening is important because colon cancer doesn’t cause symptoms in early stages. And early detection improves the odds of a cure. According to the U.S. Preventive Services Task Force, screening for colon cancer should begin as early as age 45 for people with an average risk for colon cancer.
Blood tests are recommended for people with average risk for colon cancer who choose to opt out of other approved screening measures (more on this below). These tests aren’t intended for people at high risk for colorectal cancer.
It’s a good idea to know about colon cancer risk factors and to discuss them with a healthcare professional. They can help you understand your individual risk and choose the best screening method for you.
Does colon cancer show up in routine blood work?
No. Routine blood work doesn’t include tests to detect colon cancer.
Comparing the blood tests for colon cancer
There are two blood tests currently approved by the FDA for colon cancer screening: Epi proColon and Shield.
For both blood tests, a healthcare professional draws a blood sample and sends it to a laboratory. They require no bowel preparation or special diets.
Epi proColon
What: Epi proColon was the first FDA-approved blood-based screening test for colon cancer in 2016. This test looks for DNA released from cancer cells into the bloodstream. Results usually come back in about a week.
Who: This test is available for adults ages 50 and older who are at average risk for colon cancer. It’s also for those who decline or are unable to participate in a colonoscopy.
Accuracy: The sensitivity of the test in clinical studies was around 70%. This means it picked up colon cancer in 7 out of 10 people who had it. The rate of false positives with Epi proColon is around 20%. This is when the test is positive, but there’s actually no cancer. The rate of false positives for this test likely increases with age.
Shield
What: Shield was approved by the FDA in July 2024 as a screening tool for colon cancer. This test looks for changes in DNA sequencing and mutations that cancer cells release into your blood.
Who: It’s suggested for adults who are ages 45 and older and who are at average risk for colon cancer. It’s also for those who decline or are unable to participate in a colonoscopy for a variety of reasons. This could be related to cost, scheduling, other medical conditions, or the inherent risks of the procedure
Accuracy: In a study, Shield found colorectal cancer in 83% of people (sensitivity). But the test wasn’t as good at finding advanced pre-cancer cells. It detected them in only 13% of people who had them. About 10% of people may have a false positive test result.
Other colon cancer screening methods
Since blood tests for colon cancer aren’t always accurate, it’s good that there are other screening options for colorectal cancer.
Stool tests
Stool tests check your poop for blood, which could indicate cancer, or cancer DNA. You can do them at home and send the test off to a lab. Some types of stool-based tests include:
Fecal immunochemical test (FIT)
Guaiac-based fecal occult blood test (gFOBT)
Stool DNA test
Scope procedures
The best way to screen for colon cancer is with a test to see directly inside the colon. A trained healthcare professional like a gastroenterologist can look for cancer, polyps, or bleeding. These procedures are a bit more involved than blood or stool tests. These include:
Colonoscopy: This test allows a healthcare professional to see inside the entire large intestine.
Sigmoidoscopy: This test is similar to a colonoscopy, but it only looks at the rectum and the lower half of the colon.
Capsule endoscopy: This involves swallowing a capsule that records the inside of the gastrointestinal tract. It’s more common for stomach and small intestine problems. But it’s an option if you’ve previously had an incomplete colonoscopy or you can’t have a colonoscopy due to medical issues.
These tests require you to follow a specific diet beforehand and completely empty the colon with bowel preparation for best results.
How do blood tests compare to other colon cancer screening methods?
Each of these screening tests has different requirements. Below is a table of some of the benefits and limitations to each of these tests.
Pre-test diet | Bowel prep | Sedation required | At-home test | Invasive | Recommended frequency of test | |
Colonoscopy | Yes | Yes | Yes | No | Yes | Every 10 years |
Sigmoidoscopy | Yes | Yes | No | No | Yes | Every 5 years |
FIT test | No | No | No | Yes | No | Every year |
gFOBT | No | No | No | Yes | No | Every year |
Stool DNA test | No | No | No | Yes | No | Every 3 years |
Blood tests | No | No | No | No | Yes | Every 3 years |
Colonoscopy is the recommended choice for screening, since it can detect polyps that may become or are already cancerous. It may be more expensive and is more time-intensive from preparation to post-procedure.
On the other hand, other screening measures aren’t as good as a colonoscopy (blood tests have roughly the same sensitivity as FIT testing). The other measures also require more frequent testing. Anyone with a positive result with a blood or stool test should follow up with their healthcare team for next steps to confirm the results.
You should talk with your healthcare team about your personal risk for colon cancer before choosing any screening option.
The bottom line
Blood tests are a noninvasive option for colon cancer screening in people who are at average risk for colon cancer. They’re less sensitive than a colonoscopy, but they may appeal to those who refuse or can’t do a colonoscopy. If you get a positive result on a blood test, you should follow up with a colonoscopy for confirmation. Your healthcare team can help you understand your risks and decide which screening option is best for you.
Why trust our experts?
References
American Cancer Society. (2024). Colorectal cancer screening tests.
American Cancer Society. (2024). Treatment of colon cancer, by stage.
Chung, D. C., et al. (2024). A cell-free DNA blood-based test for colorectal cancer screening. The New England Journal of Medicine.
Kavalukas, S. (n.d.). Colonoscopy versus FIT-fecal DNA for colon cancer screening. American College of Surgeons.
MedlinePlus. (2024). SEPTIN9 gene.
National Institute of Diabetes and Digestive and Kidney Diseases. (2024). Flexible sigmoidoscopy.
Robertson, K. D., et al. (2023). Capsule endoscopy. StatPearls.
Shirley, M. (2020). Epi proColon for colorectal cancer screening: A profile of its use in the USA. Molecular Diagnosis and Therapy.
U.S. Food and Drug Administration. (2024). Shield–P230009.
U.S. Preventive Services. (2021). Colorectal cancer: Screening.
University of California Los Angeles Health. (2022). The difference between screening and diagnostic tests.
Van den Puttelaar, R., et al. (2024). Effectiveness and cost-effectiveness of colorectal cancer screening with a blood test that meets the Centers for Medicare and Medicaid Services coverage decision. Gastroenterology.
Voss, A. (2024). Colorectal cancer screening: Where does the shield liquid biopsy fit in? National Cancer Institute.
