New Blood Test for Colorectal Cancer: What to Know

A new blood test to detect colorectal cancer should make screening easier for people who are reluctant to get a colonoscopy or use at-home tests.

“The blood test is an option for patients who are hesitant about traditional screening methods,” says Gregory Cooper, MD, a gastroenterologist and co-program leader for Cancer Prevention and Control at University Hospitals Seidman Cancer Center. The blood test is not a replacement for colonoscopy, which remains the best way to find tumors and prevent cancer by removing precancerous polyps.

What is the New Test?

The FDA recently approved the test, called Shield, for adults age 45 and older who are at average risk for colorectal cancer. The Shield test detects DNA fragments in the blood from cancer cells and large polyps.

A study showed the test was 83 percent effective in finding colorectal cancers. It works best at finding late-stage cancers, but detected only 13 percent of advanced adenomas, a type of precancerous polyp. These large polyps are more likely than smaller polyps to turn into cancer.

“The blood test is very good at picking up later-stage cancers, but where it falls short is detecting early-stage cancers,” says Dr. Cooper. “More importantly, it didn’t do a good job picking up advanced adenomas.”

By comparison, colonoscopy screening picks up 95 percent of dangerous polyps and can remove them, while the best stool-based home tests detect around 40 percent of precancerous polyps.

More Options to Boost Cancer Screenings

Colorectal cancer is the second-most common cause of cancer deaths in the country, yet many people who should be screened for the disease are not. A recent survey found only 59 percent of people aged 45 and older were up to date on colorectal cancer screening in 2021.

Patients may skip colonoscopy screening for a number of reasons. The tests require time off work and prescribed bowel preparation, anesthesia, and a driver to take the patient to and from the appointment.

The hope is that a simple blood test will encourage more people to be screened, even if the screening test doesn’t detect all cases of cancer. “There’s an old saying, the best screening test is the one that gets done,” says Dr. Cooper.

“If a patient declines colonoscopy, I would recommend the Cologuard (stool test). If they don’t want to do that, I would offer the blood test.”

A positive blood test isn’t a diagnosis of colorectal cancer. It means a colonoscopy is needed to find any cancer or precancerous polyps. The blood test can result in a false positive 10 percent of the time, about the same as with Cologuard.

Starting last year, follow-up colonoscopies after a positive stool test became fully covered by insurance under the Affordable Care Act. Medicare and private insurance companies are expected to cover the cost of the new blood test, as well any follow-up colonoscopies needed after a positive result.

Related Links

The board-certified gastrointestinal physicians and surgeons at University Hospitals are leaders in screening, diagnosing, managing and treating all types of colon polyps, colon cancer and other gastrointestinal conditions. Learn more about colon cancer screening services at University Hospitals.