Inadequate bowel-cleansing before a colonoscopy can result in high miss rates for precancerous polyps (adenomas) and a need for earlier repeat tests, a new study finds.
"Our findings of a miss rate of 42 percent for all adenomas and 27 percent for advanced adenomas suggest that suboptimal bowel preparation has a substantial harmful impact on the effectiveness of colonoscopy, and follow-up examination within one year should be considered," said study lead author Dr. Benjamin Lebwohl of Columbia University Medical Center in New York City.
Since colorectal cancer develops slowly over time, effective screening and early detection of the disease is key to a patient's survival. Colonoscopy screening enables doctors to identify and remove precancerous polyps (small growths in the colon) before they turn into cancer. In order for this procedure to be effective, however, patients' bowels must be thoroughly cleansed so that doctors can spot any abnormalities.
The success of the bowel "prep" depends largely on individual patients, who have to carefully follow instructions about taking medication at home in liquid or tablet form that causes diarrhea, thereby emptying the colon.
This preparation takes an average of 16.5 hours, according to a Harvard Medical School guide to the procedure, and may involve consuming up to a gallon of an oral solution containing the medication the day before the colonoscopy (while consuming only clear liquids during that day), avoiding nuts, seeds and insoluble fiber up to three days before the procedure, and fasting for six hours or more in preparation for it.
In conducting the study, published in the June issue of GIE: Gastrointestinal Endoscopy, researchers reviewed the bowel preparation quality of 12,787 patients who underwent colonoscopy at Columbia over the course of roughly two years. They found preparation quality was either poor or fair for 24 percent, or about 3,000, of those patients.
Among those with inadequate bowel preparation, 17 percent needed a repeat colonoscopy within three years. The repeat procedures (with proper bowel preparation) uncovered 198 precancerous polyps. Of those polyps, 83 were only spotted during the follow-up colonoscopy -- revealing a miss rate of 42 percent.
For the colonoscopies repeated in less than one year, the miss rate for adenomas was 35 percent and for advanced adenomas, 36 percent, the researchers said.
The findings suggest that the success of colorectal cancer screening programs hinges on proper testing techniques, including bowel preparation, the researchers said in a news release from the American Society for Gastrointestinal Endoscopy.
Current guidelines that specify recommended intervals between colonoscopies presume optimal bowel preparation, the study authors said in the news release. In cases of insufficient bowel cleansing, the decision of when to repeat the test is left to the individual physicians doing the colonoscopies.
Repeating tests at more frequent intervals increases the overall cost of colonoscopy, they added.
SOURCE: American Society for Gastrointestinal Endoscopy, news release, June 13, 2011
By Genevra Pittman
NEW YORK (Reuters Health) - A new study adds to evidence that people who get screened for colon cancer are less likely to end up dying of the disease. But it matters what doctor performs the test, researchers found.
Older Americans who'd had a colonoscopy had the lowest chance of dying from colon cancer when the test was done by a gastroenterologist, compared to a surgeon or primary care doctor.
Researchers said that could be because the digestive system specialists get extra training in colonoscopies, so they may have more experience spotting early signs of cancer than other docs. But it doesn't mean patients should forgo colonoscopy if they can't find a gastroenterologist.
"If you have a colonoscopy and the only feasible option is to go to a surgeon, let's say, it should be protective -- the odds are they're not going to miss anything significant," said Dr. Gregory Cooper, a gastroenterologist with University Hospitals Case Medical Center in Cleveland, Ohio.
"Having a colonoscopy by a non-gastroenterologist is probably still a lot better than not having one at all," Cooper, who wasn't involved in the research, told Reuters Health.
For the new study, researchers led by Dr. Nancy Baxter from St. Michael's Hospital and the University of Toronto looked at the Medicare billing records for more than 9,000 people who were diagnosed with colon cancer in their 70s and 80s and ultimately died of the disease.
The research team used the records to determine which of those people, along with another 27,000 of the same age and gender without colon cancer, had gotten a colonoscopy in prior years.
During a colonoscopy, a doctor uses a probe to check the intestine for pre-cancerous polyps and early signs of cancer, and can remove anything that looks worrisome.
Overall, the findings are in line with previous research suggesting a benefit for screening: people who died of colon cancer were 60 percent less likely to have had a colonoscopy over the previous decade, compared to the colon cancer-free group.
The majority of colonoscopies in the study were performed by gastroenterologists -- which is consistent with current practice, according to Cooper. He said those specialists do about two-thirds of the exams in the United States, followed by surgeons.
Compared to people who hadn't been screened, those who had their colonoscopy done by a gastroenterologist were also least likely to die from colon cancer.
They had a 65 percent lower risk of colon cancer death than the un-screened, compared to a 57 percent lower risk after screening by a primary care doctor and a 45 percent lower risk when colonoscopy was done by a surgeon.
The study, published in the Journal of Clinical Oncology, can't tell what caused that disparity, just as it can't prove that the colonoscopies saved any lives.
For example, "there may be real differences in patients who go to gastroenterologists versus other physicians and this may also have affected our results," Baxter told Reuters Health in an email.
Cooper said doctors training to be gastroenterologists do hundreds of colonoscopies in the years after medical school.
And what's most important for thorough screening, he added, may be how many colonoscopies doctors have done in their career, how they were trained and their so-called adenoma detection rate -- or how many of their procedures end with polyp removal.
All of those are questions patients should feel free asking their doctors, Cooper said.
"These quality metrics are more likely to separate good from poor performers better than specialty designation alone," she said.
SOURCE: http://bit.ly/KYr6mJ Journal of Clinical Oncology, online June 11, 2012.