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8 Things to Know About the Blood Test for Colon Cancer

July 31, 2024

The U.S. Food and Drug Administration (FDA) has approved Shield, a new blood test for colon cancer screening developed by Guardant Health.

What does this mean for you, and will it replace your colonoscopy?

We went to Amanda Ayers, MD, a colon and rectal surgeon with the Hartford HealthCare Digestive Health Institute, for answers.

Colon cancer screening can save your life.

Colorectal cancer is the second leading cause of cancer death in the U.S. Each year there are an estimated 150,000 new cases.

“Colon cancer has the best outcomes when discovered early, often before symptoms develop,” says Dr. Ayers. “This is why screening is so important, yet only 59% of people nationally are up to date.”

The new recommended age to begin colon cancer screening is 45. While colonoscopy is effective for screening and prevention, it can present barriers for some patients.

> Related: 4 Ways to Screen for Colon Cancer Without a Colonoscopy

Is the Shield blood test right for you?

If you’re hesitant about undergoing a colonoscopy or stool-based tests, the Shield blood test might be an option.

To provide clarity, we consulted Dr. Ayers.

While this discussion should start with your doctor, she shares these top 8 things you need to know about Shield:

1. It’s a unique blood test.

The Shield test detects colorectal cancer by identifying specific DNA fragments shed by large polyps or cancers. No other blood test looks for this DNA.

2. There’s no diet or prep required.

Shield requires no fasting, diet changes or preparation.

3. The test is only for average-risk patients.

The Shield test is meant for adults aged 45 and older at average risk for colorectal cancer.

4. It’s not for high-risk individuals.

“Patients with symptoms like bleeding, changes in bowel habits or abdominal pain are not candidates,” explains Dr. Ayers.

“Those with a family history of colon cancer, inflammatory bowel disease, cancer history or hereditary cancer predisposition are also excluded.”

5. It has 83% sensitivity.

“This means that 83% of patients with colon cancer confirmed by colonoscopy had a positive Shield test,” says Dr. Ayers.

How does that compare with other colonoscopy alternatives?

“Colonoscopy and multi-targeted stool DNA tests (Cologuard®) are 92-95% sensitive. Fecal immunochemical test (FIT) is about 74%, and Epi proColon® is only 50%.”

6. It’s less effective for polyps.

“The Shield test is good at finding cancers but not as effective at detecting polyps. Colonoscopy is superior for finding and removing polyps before they become cancerous,” says Dr. Ayers.

7. Follow-up is required.

You won’t be able to avoid a colonoscopy completely if your test is positive.

“A positive Shield test absolutely requires a follow-up colonoscopy to determine the size and location of any lesions for further treatment consideration. Confirmation with a colonoscopy is essential,” emphasizes Dr. Ayers.

8. This test is not for symptomatic patients.

The Shield test is a screening tool for average-risk patients. If you have symptoms, see your doctor for evaluation.

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A colonoscopy is still the best option for screening.

A colonoscopy offers both screening and prevention benefits.

“Colonoscopy is still the gold standard,” says Dr. Ayers. “It can identify lesions, remove polyps (depending on size), and determine whether a polyp is cancerous, as well as its location and size.”

Talk to your doctor about the best screening option for you.

Every patient is unique.

“That’s why it’s important to review the best test for you based on your individual health, family history, symptoms and preference,” explains Dr. Ayers. “Each test has its own pros and cons, and this is a personalized decision.”

There are also many misconceptions about tests like colonoscopies, including their risks and procedures. But it’s important.

Don’t get bogged down with the fine print if this seems overwhelming.

“Instead, focus on the most important thing – getting screened,” says Dr. Ayers. “The best test for colon cancer screening is the one that gets done, and this new test provides another option.”