WEDNESDAY, June 15 (HealthDay News) -- 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.
The U.S. National Digestive Diseases Information Clearinghouse
provides more information on
colonoscopy and how it is performed.