Putting Off Your Colonoscopy? Now You Can Get a Blood Test Instead

About 1 in 3 American adults who are eligible for colorectal cancer screening haven’t been tested as recommended. But detecting the disease early through screening dramatically increases survival rates.

Colorectal cancer is the top cancer killer of American adults younger than 50, making screening crucial. But many who are eligible for screening are wary of getting a colonoscopy or can't take the time off from work, says Tiago Biachi, MD, PhD, a medical oncologist in the gastrointestinal oncology department at Moffitt Cancer Center in Tampa, Florida.

“We are seeing more colorectal cancer in younger adults, and early detection truly saves lives,” says Lilian Chen, MD, the chief of colon and rectal surgery at Tufts Medical Center in Boston.

“The best screening test is ultimately the one that gets done consistently,” she says.

Colorectal Cancer Screening Options Now Include a Blood Test

Colorectal cancer usually develops slowly, over 10 to 15 years, and starts out as precancerous polyps. Screening — with whatever method people choose — lets doctors find and remove those polyps before they turn into cancer, Dr. Biachi says.

“When detected early, survival rates are excellent,” he adds.

Previous colorectal cancer screening guidelines gave people over age 45 two options: colonoscopy or stool tests. The new guidelines add a blood test for average-risk people.

Here’s an updated breakdown of the tests, based on type and how often they should be done.

Imaging Studies

• Colonoscopy, which examines the colon and rectum, done once every 10 years
• Flexible sigmoidoscopy, which examines the lower third of the colon, once every five years
• Computed tomography (CT) colonography, which creates a 3D image of the colon and rectum, every five years.

Stool Tests

• Cologuard, a next-generation ng-mt-sDNA test: An updated version of an at-home test that analyzes stool samples for certain DNA markers and hemoglobin (protein in red blood cells) specific to colorectal cancer. This is recommended every three years.
• ColoSense, an mt-sRNA test: A new at-home test that analyzes stool samples for hemoglobin and RNA markers specific to colorectal cancer. This is recommended every three years.
• High-sensitivity guaiac-based tests (gFOBT): These look for hidden blood in the stool and should be done every year.
• High-sensitivity fecal immunochemical tests (FIT): These detect blood in the lower digestive tract and should be done every year.

Blood Tests

• Shield Test This kind of test looks for specific DNA changes caused by colorectal cancer that float freely in the blood. The type of test is only recommended for people who decline or do not complete the preferred screening tests listed above. These should be done every three years.

Any stool or blood tests that are positive should be followed up with a colonoscopy within six months

Experts Say More Screening Options Were Needed

But among younger adults (ages 20 to 64), the opposite is happening, with rates increasing by as much as 3 percent each year in the same time frame.

The report also found that 75 percent of colorectal cancers diagnosed in adults under the age of 50 (called early-onset colorectal cancer) are at an advanced stage, which means they’re harder to treat and more likely to be deadly.

“Today, about 1 in 5 colorectal cancers is diagnosed in people under 55, and it has become the leading cause of cancer death for adults under 50,” Biachi says.

While doctors are still working to learn more about what’s driving this increase in cases in younger adults, it seems to be linked to modern lifestyle factors, Biachi says, including:

• Higher rates of obesity
• Less physical activity
• Diets heavy in processed foods and red meat, but low in fiber
• Increased alcohol use
• Changes in the gut microbiome

“Many of these younger patients do not have the classic risk factors like family history,” he continues. “This is why the update matters.”

The new guidelines also open the option for more practical methods of screening, says Ketan Thanki, MD, a colorectal surgeon with the MemorialCare Todd Cancer Institute at Long Beach Medical Center in California.

“Colonoscopies are expensive and time-consuming, and people often dread the prep and have a fear of complications,” he says. “Blood and stool tests avoid those issues.”

Which Colorectal Cancer Screening Tool Is Best?

Doctors say the colonoscopy is still the best way to be screened for colorectal cancer. “It remains the gold standard because colonoscopies are very good at detecting abnormal lesions, identifying exactly what those lesions are, and most importantly, are preventative, allowing doctors to remove precancerous polyps before they turn into cancer,” Dr. Thanki says.

Biachi agrees. “Get a colonoscopy every 10 years, starting at age 45, as long as you’re in good health,” he says. “This is what I recommend for most people who are willing to do it. It gives you the greatest protection.”

While blood and stool tests can screen for cancer, they can’t tell the difference between types of lesions and don’t allow doctors to remove them during screening, Thanki points out.

“My second choice would be a stool test like Cologuard, because it is very good at detecting cancers and polyps and signaling that you need a colonoscopy,” he says. “Blood tests would be my last choice as they are generally best at detecting later-stage cancers and can miss precancerous polyps and early-stage cancers.”

Biachi suggests viewing blood tests as an “entry-level option” for people who have been skipping screening regularly. Ultimately, “the right choice depends on your personality, lifestyle, and how much you value convenience versus maximum effectiveness,” Biachi says.

How ever you choose to do it, doctors stress the importance of screening for colorectal cancer. “If you’re 45 or older and haven’t started yet, talk to your doctor soon about getting screened,” Biachi says. “It’s one of the most important things you can do for your long-term health.”