The results suggest doctors should take their patients' preferences into consideration before recommending one test or the other, according to the researchers.

"The basic finding here is, when offered a choice, you not only get better screening participation, but also a significant proportion of people don't choose colonoscopy," said Dr. Linda Rabeneck, vice president of prevention and cancer control at Cancer Care Ontario, who was not involved in the research.

Rabeneck also told Reuters Health that the report, published in the Archives of Internal Medicine, shows people have a lot of different preferences when it comes to picking a test.

Led by Dr. John Inadomi of the University of Washington School of Medicine in Seattle, the new study followed 997 people who were using the San Francisco public health system between April 2007 and March 2010.

Those people were divided into three groups, all made up of men and women between 50 and 79 years old with an average risk of developing colorectal cancer.

According to the American Cancer Society, a person's risk of developing the cancer over their lifetime is about one in 20.

A number of factors can increase a person's risk, however. They include a family history of colorectal cancer, and a personal history of colon polyps or inflammatory bowel disease. People who had those added risk factors were excluded from the study.

For one group of participants, doctors only recommended colonoscopy -- a procedure that involves inserting a camera into the colon to examine intestinal walls for abnormal growths.

For another group of patients, the doctors only recommended stool testing -- formally known as fecal occult blood testing -- which measures the amount and characteristics of blood in a person's stool.

The third group's doctors gave patients a choice between the two tests.

Overall, 58 percent of the study participants got the screening test their doctors had recommended or the one they picked themselves.

But there were significant differences between the three groups.

Of the 337 people whose doctor had recommended a colonoscopy, just 38 percent actually had one over the next 12 months. That compares to 344 people whose doctor recommended a fecal occult blood test -- 67 percent of them got that test.

When the third group of 321 people was given a choice between the two forms of colon cancer screening, 69 percent had the test they had picked -- 122 opted for the stool test and 99 picked colonoscopy.

For those who picked the fecal occult blood test, the researchers did not consider their screenings complete if they tested positive but didn't get a follow-up colonoscopy to investigate further. Eight people who had the stool test got positive results, and three of those did not get a colonoscopy afterwards.

"There are a lot of factors that are associated with the choice of one test over another," Rabeneck told Reuters Health. "I think this drives it home in a very powerful way."

African Americans were the least likely to get screened at all, while Asians and Latinos were the most likely. Non-whites were also more likely to follow through with stool testing, while whites were more likely to actually get a colonoscopy.

Personal preferences will also play a role in a patient's choice, researchers say.

"Some will prefer a test that's easier and done at home. Some will prefer a colonoscopy and all that goes along with it," said Rabeneck.

According to the U.S. Preventive Services Task Force, a government-backed advisory group, people ages 50 to 75 should be screened by one of three methods: a colonoscopy every 10 years; annual stool testing; or a less-thorough look into the colon (known as flexible sigmoidoscopy) every five years in conjunction with stool testing every two to three years.

Inadomi's team originally expected that giving patients a choice would confuse or overwhelm them and potentially discourage them from making any decision or getting any test.

Based on their study's results, Inadomi told Reuters Health in an email he now thinks doctors should give patients choices.

"I would make sure that I took into account the patient's preferences. I would flat out describe these tests… I think this goes against what a lot of us are doing right now. We should be finding out what patients prefer and really pursuing that," Inadomi said.

"The study…demonstrates that not having enough choice may lead to inaction when the only choice is colonoscopy," wrote Dr. Theodore Levin, from Kaiser Permanente Medical Center in Walnut Creek, California, in a commentary accompanying the article.

Inadomi's team also notes that they did their best to reduce barriers to getting the tests, which included providing rides.

"We need to realize that if you provide access and an infrastructure even in a low income, low education environment you can get good compliance," he said.

SOURCE: bit.ly/HsLD0u Archives of Internal Medicine, online April 9, 2012.

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