Shield™ Blood Test vs. Colonoscopy for Colon Cancer
Shield™ vs Colonoscopy. We’ve been listening to all the questions buzzing around about colon cancer screening options. Questions like, ‘What’s up with this new blood test that can detect colon cancer?’ We’d like to answer some of your top questions about blood-based colorectal cancer screening so you can stay informed. This blog will compare Shield ™ blood test to colonoscopy so you can make informed decisions about your colon health.
1. Question: What is the Shield™ blood test?
Answer: This new FDA-approved blood-based screening test for colon cancer can detect microscopic traces of colorectal cancer DNA when tumors are present. As tumors shed genetic material, depending on the stage of growth, these fragments can be detected in the bloodstream. However, with stage 1 colorectal cancer, the detection rate is 55 percent with the blood test. This translates to missing 45 percent of stage 1 colon cancer cases.
The Shield™ test will also miss 87 percent of advanced adenomas that are serious pre-cancerous lesions, says Raul Cubillas, MD, gastroenterologist with Gastroenterology of the Rockies. “Colonoscopy detects 95 percent of colon cancer and only misses 5 percent. It also detects about 85 percent of advanced adenomas and only misses 15 percent,” Dr. Cubillas added.
2. Question: Is the Shield™ blood test as good as a colonoscopy?
Answer. No. It is not. Dr. Cubillas goes on to explain the limitations of blood-based colorectal cancer screening.
“The main limitation of this test is that the performance to detect stage I colon cancer and advanced adenomas is much lower than colonoscopy,” Dr. Cubillas said.
“Prevention of colon cancer depends on detection of colon cancer at early stages (like Stage I) or detection of polyps with a higher chance of compression into cancer (advanced adenomas).”
Answer: People who meet these criteria might be eligible for the blood-based screening test for colon cancer.
Men and women 45 or older with average risk for colon cancer who are asymptomatic. Dr. Cubillas reminds readers that this test should only be used for patients who have no symptoms as part of screening for colon cancer.
4. Question: Who is not eligible for blood-based testing for colorectal cancer?
Answer: People with the following criteria are not candidates for the blood test. This is because the patient has a risk above average for colon cancer.
Personal history of pre-cancerous polyps
Prior history of colorectal cancer
Family history in first degree relatives at any age or two second degree relatives younger than 50
Symptoms like rectal bleeding, weight loss, diarrhea or anemia
Inflammatory Bowel Disease
Lynch Syndrome
5. Question: What can a colonoscopy find that the Shield™ blood test cannot?
Answer: Colonoscopy continues to be the gold standard for detection and prevention of colon cancer. Here’s why.
Colonoscopies will detect 95 percent of cases of stage I colon cancer. It only misses 5 percent.
“Colonoscopies will detect 85 percent of advanced adenomas – these are a series of precancerous polyps,” Dr. Cubillas said. “The Shield™ blood test has a performance that is not as good as a colonoscopy. It only detects 55 percent of stage I Colorectal Cancer (CRC) and only 17 percent of advanced adenomas.”
Furthermore, the maintenance sensitivity to detect any kind of adenomas of any size is lower than 17 percent, [with the blood-based CRC test]. When colon cancer is detected in the early stage, which is the main target of screening procedures, the outcome is much better, says Dr. Cubillas.
In their position statement, the American College of Gastroenterology (ACG) reports, “A one-time Shield™ test may fail to detect one in three early-stage cancers and one in six total cancers.”
ACG also shared an excerpt from an editorial authored by Dr. Gloria Coronado and Dr. David Lieberman that the ACS also published in CA: A Cancer Journal for Clinicians: “Because blood tests are less likely to find advanced adenomas than other available tests, the use of these tests in place of more effective screening tests could result in net harm (i.e., increased deaths from colorectal cancer).”
Want to learn more about colonoscopy screenings? Explore our colonoscopy screening page.
6. If my Shield™ test is negative, do I still need a colonoscopy?
Doctor explaining colonoscopy results to patient using monitor images on screen.
Answer– A negative test result from the blood test means the test did not detect colorectal cancer or advanced adenomas.
However, this negative test result does not guarantee that a person who tests negative does not have colon cancer. Instead, it simply means the test did not indicate detection of cancer, according to patient literature published by Shield™.
The maker of blood-based colorectal screening tests goes on to report, the blood test has a 17 percent false negative result.
This means that 17 out of 100 people will incorrectly receive a negative test result, based on data reported in the blood-based screening patient literature. Source: FDA, Fact Sheet
7. Question: If my Shield™ test is positive, what happens next? Do I need a colonoscopy?
Answer: If your test is positive that does not mean that you have colon cancer or an advanced adenoma. However, patients with positive results should have a colonoscopy to confirm the presence of colon cancer or an advanced adenoma, says Dr. Cubillas. The false positive rate for colon cancer is 10 percent. This means that 1 out of 10 patients who have a positive result do not have colon cancer.
8. Question: Can the blood-based CRC screening miss colon cancer?
Answer: Yes.
Stage 1- Colorectal Cancer – Clinical trials indicate a detection rate of 55 to 65 percent with the blood test
Precancerous lesions– the blood test cannot detect 87 percent of this type
9. Who might want to choose blood-based screening for CRC instead of colonoscopy?
Average-risk patients with no family history of colon cancer
Patients reluctant to undergo colonoscopy
Patients seeking an alternative screening option
1o. What if I don’t have insurance or have a high deductible? Because of my financial situation, should I get a blood test?
We understand that insurance coverage and your personal finances may influence which colon cancer screening test appeals to you. Consider discussing this with your doctor so that you’re aware of the pros and cons of various screening options. This gives you a chance to understand the documented limitations linked to the blood test screening option.
Generally, the blood test may be an option for some average-risk adults.
As mentioned in this article, the blood test comes with some limitations, when compared to colonoscopy. Blood-based CRC tests can detect colon cancer, but doesn’t detect colon polyps or remove them.
Colonoscopy is the only test that can detect and possibly prevent colon cancer by removing pre-cancerous polyps—making it the gold standard in colon cancer screenings.
If you have questions about colorectal cancer screening options, please reach out to our GI specialists today. We’re here to answer your questions.
Co-written by Elise Oberliesen, digital marketing specialist and Raul Cubillas, MD, gastroenterologist, with Gastroenterology of the Rockies. Medically reviewed by Tamas Otrok, MD, gastroenterologist, June 26, 2026.
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