May 12, 2010 -- Some doctors who perform colonoscopy exams are better than others at spotting precancerous polyps, and now new research confirms this skill is associated with better outcomes.
The study found that colorectal cancers were less likely to be diagnosed during the time between scheduled colonoscopy exams when the doctor performing the test had a detection rate of benign polyps of at least 20%.
That means that for every 100 colonoscopy procedures performed, the doctor found one or more precancerous polyps (adenomas) during screening at least 20% of the time.
The research appears in the May 13 issue of the New England Journal of Medicine.
"The adenoma detection rate is an accepted quality indicator for colonoscopy, but until now it has not been proven to be associated with lower rates of colorectal cancer," study co-researcher Jaroslaw Regula, MD, of Poland's Institute of Oncology tells WebMD.
Colonoscopy screening involves a thin, flexible, illuminated tube with a tiny video camera that is threaded through the colon to look for evidence of cancer or precancerous polyps. When suspicious polyps are found, they are removed during the procedure.
While it is clear that colonoscopies save lives, it has long been recognized that the quality of the exam is highly dependent on the skill of the doctor who performs it.
Because of this, various indicators have been proposed to assess physician skill.
In addition to adenoma detection rate, measuring how often the doctor is able to reach the beginning of the colon, or cecum, is also used to assess exam quality.
Assessing Colonoscopy Quality
In the newly published study, Regula and colleagues investigated how well these quality assessment measures predict colorectal cancer risk during the period between initial and follow-up examination.
They analyzed the records of 186 doctors in Poland who performed about 145 colonoscopies each from late 2000 through 2004.
Their average adenoma detection rate was around 12%, and their average rate of reaching the cecum was 94%.
Reaching the beginning of the colon was not associated with the diagnosis of colorectal cancer before scheduled follow-up screening in the study, but adenoma detection rate definitely was.
Forty-two such cancers were identified among about 45,000 patients screened, but only one of these occurred in a patient whose exam was performed by a doctor with an adenoma detection rate above 20%, Regula says.
"The risk was significantly higher among patients whose colonoscopies were performed by [doctors] with detection rates of less than 20%," he says.
Regula says doctors who perform colonoscopies should keep track of their adenoma detection rate and provide this information to patients.
"Certainly if patients start asking for this kind of data, it may start happening more," he tells WebMD.
While the Polish study failed to show the value of making it to the beginning of the colon as a measure of exam quality, Brooks says other studies suggest a benefit.
Studies have also shown that the more time a doctor takes to examine the colon as the tube is withdrawn, the better.
It is recommended that doctors take at least six minutes for the withdrawal phase of a colonoscopy. A recent assessment of this practice found that those who did this identified significantly more polyps than those who took less time.
"It is now clear that polyps missed on the way in can be detected with careful examination on the way out," he says.
Brooks says people who have had colonoscopies can have confidence in the findings, even if they don't know their doctor's adenoma detection rate or withdrawal time.
"I would hate for people to think their colonoscopy was worthless," he says. "This is a very effective tool for identifying and preventing cancer."