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Increased access to computed tomography ( CT ) colonography did not reduce the number of conventional colonoscopies at a large university hospital, researchers said at Digestive Disease Week (DDW) 2010.

"Five years after the initiation of a CT colonography colorectal screening program at our institution, optical colonography remains the predominant screening modality for colorectal cancer," said Patrick Pfau, MD, University of Wisconsin, Madison, Wisconsin.

In 2004, the University of Wisconsin became the first institution in the United States to have third-party payer coverage of CT colonography for average-risk colorectal cancer screening, he said.

So the researchers sought to determine the effect of the CT screening program on the number of conventional colonoscopies performed among patients aged 50 to 75 years from 2003, the year before CT colonography became eligible for insurance coverage, to 2009.

The mean number of optical colonography exams per quarter increased significantly from 1,104 in 2003 to 1,976 in 2008 (P < .001).

For CT colonography, the highest quarterly count was 307 in the third quarter of 2005. By the end of 2008, the figure had declined to 203 per quarter, Dr. Pfau said.

In 2009, only 8.5% of screenings utilised CT colonography. A total of 86.6% of all colorectal screening exams were performed with optical colonoscopy, he said. The other screens were faecal occult blood or immunochemical tests.

The number of therapeutic colonoscopies remained basically unchanged over the 5-year period, with a quarterly mean of 463 in 2003 and 490 in 2009 (P = .36). Therefore the increase in optical colonoscopies cannot be attributed to procedures triggered by abnormal CT colonography results, Dr. Pfau said.

The findings challenge "theoretical modelling studies that showed that once virtual colonoscopies [as CT colonography is often called] became accepted as a national screen test, regular colonoscopies would be reduced by 25%," Dr. Pfau said.

But the results may not be generalisable to the rest of United States and Canada, as the university serves an area that is of higher-than-average socioeconomic status, he said.

At a press conference, Dr. Pfau speculated that once the details of CT colonography are explained to patients, the "virtual" procedure might not longer be as appealing as it first sounds.

"Many patients mistakenly think that CT colonography does not require bowel preparation," he said. "And they fail to realise, until told, that they will still need a regular colonoscopy to confirm and treat positive findings. Once they understand this, their enthusiasm for CT colonography often fades."

Source: DDW

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