BOSTON — The American Cancer Society added a blood test called Shield to its recommended screenings for colorectal cancer for the first time on a Wednesday in 2024. The test, developed by California-based Guardant Health, was approved by the Food and Drug Administration earlier this year.

The Shield blood test detects DNA fragments released by cancerous tumors and is 83% effective in identifying colorectal cancers. However, it is less effective at detecting early-stage disease, when treatment is most successful, and cannot detect precancerous polyps because they do not release the DNA fragments the test targets. There is no data yet showing whether the test can reduce deaths from colorectal cancer over time.

The American Cancer Society recommends the Shield test only for people who cannot or will not undergo more effective screenings like colonoscopies or stool-based tests such as Cologuard or ColoSense. Colonoscopy remains the most effective screening method, as it allows doctors to find and remove precancerous growths during the procedure. Stool tests, which require collecting samples at home and sending them to a lab, are also more established options that do not involve blood draws or expensive equipment.

“About a third of Americans are not up to date with colorectal cancer screening,” said Dr. William Dahut, chief scientific officer for the American Cancer Society. He added that adding a new type of test “could dramatically increase the number of people screened for colorectal cancer, which is the nation’s top cause of cancer death in people under age 50.” Dahut noted, “The Shield blood test won’t be as good at picking up the pre-cancer areas or stage 1 cancers, but it’s certainly much better than not being screened at all.”

Other experts expressed measured support. “Getting screened for colorectal cancer is more important than ever,” said Dr. Kimmie Ng, director of the Young-Onset Colorectal Cancer Center at Dana-Farber Cancer Institute. She added, “Having a variety of different screening options available to people to encourage uptake of screening is really quite important.”

Some physicians raised concerns about potential misuse. “This is better than nothing, for sure,” said Dr. Scott Kopetz, a gastrointestinal medical oncologist at the University of Texas MD Anderson Cancer Center. “The concern is that we’re going to lose ground in our battle for colorectal cancer prevention and early detection, that this is going to reduce the quality of screening that some of these patients may otherwise have received, because there is such a demand for what’s easy and fast.”

The Shield test costs $895 out of pocket and should be performed every three years. Insurance coverage is not guaranteed, as it typically follows a recommendation from the U.S. Preventive Services Task Force, which has not yet issued guidance on the test. A positive result from either Shield or a stool test requires a follow-up colonoscopy. Colorectal cancers are rising, especially among adults under 65, with more than 157,000 new cases expected in the U.S. in 2024. The American Cancer Society recommends that all average-risk adults begin screening at age 45.