Nearly 700 people who had colonoscopies at the Lakeshore General Hospital in Pointe-Claire, Que., are being asked to undergo new tests because the old results may be incomplete.

The West Island Health and Social Service Centre, the health agency that oversees the hospital, said the possibly deficient tests were conducted between 2009 and this year.

"The retaking of tests follows a detailed analysis done by the health and social service centre," said Dr. Richard Germain, chairman of the agency's physicians, dentists and pharmacists committee.

The move is a preventative measure to allay patients' and doctors' concerns, because colonoscopies performed by one physician in particular might not have examined the colon all the way to its upper end. Hospital officials stressed that they weren't certain the colonoscopies were deficient, just that the medical files didn't conclusively say that the entire colon had been examined.

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Colonoscopies performed by one physician in particular at the Lakeshore General Hospital might have been incomplete.

It's possible those tests could have missed a precancerous lesion, for example, but Nadeem Ahmed, a gastroenterologist at Lakeshore General, said the risk is far from grave.

"Colon cancers are typically thought to take five to 10 years to grow to a size that they are likely to cause problems and be of significant impact to the patient's health, but there are exceptions."

The problem came to light during quality-control checks in April.

The hospital, located on western Montreal Island, said affected patients have been notified by registered mail. They'll undergo new colonoscopies on evenings and weekends through mid-December.

Hospital officials would not disclose the name of the physician who performed the tests in question. They did say they're working with Quebec's college of physicians to investigate the matter.

The officials also said that the physician who carried out the colonoscopies stopped working at the hospital in January for unrelated reasons.