Early detection of colon cancer can potentially prevent a majority of deaths from this disease 73 percent theirs. But just 50 to 75 percent middle-aged and older adults who need regular screening to be tested.

One reason, doctors say, is that the screening methods scare many people away.

For people at average risk, there are two options: a colonoscopy every 10 years or a fecal test every one to three yearsdepending on the type of test.

Or, as Dr. Folasade P. May, a gastroenterologist at UCLA Health, says: “Either you take this horrible laxative and then a doctor puts an instrument on your butt, or you have to manipulate your own poop.”

But something much simpler is in store: a blood test. Gastroenterologists say such tests could become part of the routine blood tests that doctors order when someone comes for an annual physical, for example.

“I think this is going to take off,” said Dr. John M. Carethers, a gastroenterologist and vice chancellor for health sciences at the University of California, San Diego.

About 53,000 Americans are expected to die from colorectal cancer this year. It is the second most common cause of cancer-related deaths in the United States, and while the death rate has decreased among older adults, it has increased among people under age 55.

Current guidelines recommend screenings from age 45. The problem is causing more people to get screened.

Enter the blood test. It takes advantage of the discovery that colon cancer and large polyps – clumps of cells lining the colon that occasionally turn into cancer – release fragments of DNA in the blood.

a study published Wednesday in The New England Journal of Medicine found that a blood test that looks for such DNA, called Shield and made by the company Guardant Health, revealed 87 percent of cancers were in early and curable stages. The false positive rate was 10 percent.

“This will be big news,” said Dr. May, an advisor to Exact Sciences, maker of the Cologuard fecal test.

But there’s a caveat to the blood test: Although it detects cancers, it misses most large polyps; he finds only 13 percent of it. In contrast, the fecal test detects 43 percent and a colonoscopy finds 94 percent, said Dr. Carethers.

Although polyps are usually harmless, a few can turn into cancer. Therefore, doctors want to find and remove them all to prevent the formation of cancer.

Dr. Barbara Jung, chair of the department of medicine at the University of Washington and president of the American Gastroenterological Association, said patients should be fully informed before opting for a blood test. In particular, they need to understand that while this test helps detect cancer at an early stage, it does not prevent it because it is not good at detecting precancerous polyps.

“We need to have that discussion,” with patients, she said. But, she added, “much of this will end up with GPs who already have very little time to get through a litany of screenings and counselling.”

Doctors will also need to explain to patients that if the blood test result is abnormal, they should schedule a colonoscopy to detect polyps or cancer early and remove them if they are present.

It is also not clear how often people should take the blood test. Guardant suggested every three years, but that recommendation is not well supported, Dr. Jung said.

Dr. Jung added that she would like to know whether the blood test performs well in people who are too young to qualify for existing screening tests. But this requires additional research. She is concerned about the rising rates of colon cancer among younger people. It would be “very attractive,” she said, if people could get a blood test for colon cancer at age 30.

“That would be my biggest excitement,” said Dr. Jung.

The big unknown, however, is the costs. Guardant has applied to the Food and Drug Administration for approval to commercialize the test. The company now sells it as a “laboratory-based test,” which does not require FDA approval but is also not covered by health insurance. For those who want to pay out of pocket, the price is $895. But, said Matt Burns, a spokesman for Guardant, the company will work with Medicare and Medicaid and private insurers to “finalize prices” if they become approved, said Matt Burns, a spokesman for Guardant.

Dr. William Grady, the medical director of the Fred Hutchinson Cancer Center’s Gastrointestinal Cancer Prevention Program who is a corresponding author on the Guardant-sponsored study, said the company might settle on a price that makes it comparable to the price of the other screening methods. The costs of the Cologuard fecal test $581 to $681. Colonoscopies, which are usually needed half as often, tend to cost $1,250 to $4,800, although some hospitals charge more. The average cost of a colonoscopy in the United States is $2,750. The tests are usually covered by insurance.

Dr. May cautioned that patients should know that these three screening tests are not equivalent. With the blood test, she said, “we are moving from prevention to early detection.”

But, she said, the blood test is quite simple. When a doctor requests routine blood tests, all that needs to be done is a colorectal cancer test.

“That’s phenomenally exciting,” she said.

And the ease of use could outweigh the test’s limitations, said Dr. Carethers, who wrote an editorial team in the journal associated with the research. After all, he said, the goal of screening is to reduce the number of deaths from colon cancer for the population as a whole.

If a blood test means that many more people are screened, the result – fewer deaths from colon cancer – will be favorable.

“The best screening test is the one completed by the patient,” he wrote.