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The new research shows, duration of colonoscopy is positively linked with adenoma detection and the quality of screening, but only to a certain point.

"Our data suggest that a threshold may exist" -- between about 5 and 9 minutes -- beyond which the duration of colonoscopy "may no longer be correlated with adenoma detection," the researchers reported March 16th in an American Journal of Gastroenterology advance online publication.

"This suggests it may not matter how long you take to look at the colon; you may find more adenomas, but that doesn't translate into benefit to the patient down the line," lead author Dr. Ziad F. Gellad said.

That's because doctors who spend more time during colonoscopy are more likely to find small, clinically insignificant polyps, he added.

With CT colonography, polyps less than 6 mm in diameter are not routinely reported. "That begs the question then, why are we removing these small polyps during colonoscopy, when we're just adding to procedure time, patient risk, and cost?" Dr. Gellad said.

He noted that colonoscopy duration, often described as "withdrawal time," is a proposed quality indicator for colonoscopy. In 2002, the U.S. Multi-Society Task Force recommended that withdrawal time for normal colonoscopies should average 6 to 10 minutes.

Dr. Gellad, from Duke University Medical Center, Durham, North Carolina, and his associates had originally theorized that withdrawal time at a baseline exam would be inversely correlated with the risk of finding neoplasia 5 years later.

Their study involved 1193 participants in Veterans Affairs Cooperative Study 380, ages 50 to 75 years, who had screening colonoscopy between 1994 and 1997 and again within 5.5 years.

Withdrawal times for the baseline exams ranged from 1 to 57 minutes, with a mean of 13.2 minutes in subjects without neoplasia at follow-up vs 15.3 minutes in those with neoplasia (p = 0.18).

On logistic regression analysis, withdrawal time was not associated with the risk of interval neoplasia (p = 0.07).

At individual medical centers, average baseline exam withdrawal times (ranging from 5.2 to 25.6 min) were correlated with detection of adenomas, but not advanced neoplasia. (And if the center with the fastest average time was excluded, there was no longer any correlation with adenoma detection.)

Furthermore, the follow-up exams revealed that risk of interval neoplasia or advanced neoplasia was not related to withdrawal time of the baseline colonoscopy.

"Our results suggest that there is a limited range in which withdrawal time is a useful quality indicator for colonoscopy; this range may exist because of the increased removal of clinically insignificant polyps with increasing withdrawal times above a certain threshold," the researchers conclude.

"Developing a better understanding of the significance of diminutive polyps will be integral to the refinement of existing quality measures," they add.

Source: Reuters Health

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