How effective are colonoscopies? Once rated as the “gold standard” in detecting colon cancer, a study by Canadian researchers is raising questions about the popular procedure, according to a study published online by the journal Annals of Internal Medicine.

Researchers found colonoscopies, which involve inserting a tube in the rectum to check for potentially cancerous growths, may be less effective than doctors had thought.

In fact, the study found the procedure was little help to patients with cancer on the right side of the colon.

Dr. David Ransohoff, a professor of medicine at the University of North Carolina at Chapel Hill, who wrote a related editorial in the medical journal, said the screenings probably prevent about 60 to 70 percent of deaths from colorectal cancer, not about 90 percent as previously thought.

Still, many doctors agree colonoscopies are a crucial tool in the fight against colon cancer.

“This study raises provocative questions about the quality and limitations of colonoscopy,” Dr. David Robbins, associate chief of endoscopy at the Lenox Hill Hospital in New York said in a statement.

“While the results are not directly relevant to how colon cancer screening is performed in the U.S. in 2009, the drumbeat is clearer than ever: quality colonoscopy by experts’ saves lives. ”

In the United States, colorectal cancer is the third most common cancer diagnosed in both men and women, according to the American Cancer Society. The agency estimates more than 100,000 new cases of colon cancer and 40,000 new cases of rectal cancers will be diagnosed in 2008.

Click here to read more on this study from the journal Annals of Internal Medicine.