The FDA approved the first blood test designed to screen for colorectal cancer, called Shield, in July 2024 for adults 45 and older at average risk.
Shield offers a far more convenient alternative to colonoscopy, requiring only a simple blood draw rather than an invasive procedure requiring full bowel preparation beforehand.
A clinical study found that Shield detected colorectal cancers in 83% of trial participants who were also found to have cancer during a colonoscopy.
However, Shield’s sensitivity for detecting precancerous growths was significantly weaker, registering at only 13% in the same trial population.
Researchers estimate that about two and a half times more colon cancer deaths can be expected among people using the blood test every three years compared to those getting a colonoscopy once a decade.
Established colonoscopies and stool-based tests remain more effective at catching early-stage cancers and precancerous polyps, giving them a substantially greater projected long-term impact than blood tests.
“The first generation of blood tests are a really exciting development in the colorectal cancer screening paradigm,” said lead researcher Dr. Uri Ladabaum, a professor of gastroenterology with Stanford Medicine.
Dr. Ladabaum added a pointed caution for patients already willing to pursue more effective options: “But for now, if you’re willing and able to do a colonoscopy or stool-based test, don’t switch to a blood test.”
Medical experts warn that if too many patients currently undergoing colonoscopies or stool tests switch to blood tests, overall colorectal cancer death rates will rise considerably.
It is estimated that a third or more of the U.S. population is not following recommended colorectal cancer screening guidelines, with many living in rural or underserved communities.
Colorectal cancer remains the second-leading cause of cancer-related deaths in the United States, claiming more than 50,000 lives every year despite being largely preventable with early detection.
A colonoscopy is the only colorectal cancer screening method that can actually prevent the disease by allowing doctors to identify and remove precancerous polyps before cancer develops.
The American Cancer Society recommends Shield and similar blood tests only for individuals who are unwilling or unable to undergo more effective screening methods such as colonoscopy or stool-based tests.
