Laxative-Free CT Colonography: Still Not Good Enough

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Summary and CommentLaxative-Free CT Colonography: Still Not Good EnoughThe positive predictive value was low — particularly for polyps smaller than 10 mm.

Several studies, including a randomized controlled trial from the Netherlands (JW Gastroenterol Jan 6 2012), have now reported the performance of laxative-free computed tomographic colonography (CTC). In the current industry-supported, prospective study, investigators evaluate the performance of laxative-free CTC followed by colonoscopy in 605 adults aged 50 to 85 undergoing screening or surveillance exams. As usual, the CTC was performed after several doses of contrast ingestion, and colonoscopy was performed blinded to the results of the CTC.

Per-patient sensitivity and specificity of laxative-free CTC for polyps 10 mm in size were 91% and 85%, respectively. Sensitivity fell dramatically for lower size thresholds. For adenomas 8 mm, the sensitivity of CTC was 70% (vs. 88% for optical colonoscopy), and the positive predictive value of CTC was 26%. For adenomas or cancer 6 mm, the sensitivity of CTC was 59%, and the positive predictive value was 42%. For a confirmed polyp of any histology, the sensitivity of CTC was 59% for those 8 mm and 47% for those 6 mm.

Comment: Most experts will conclude from these results that computed tomographic colonography is not adequate as a substitute for colonoscopy. Patients typically want to know whether they have polyps in the 6–9 mm range, and if so, they want them removed. With an 85% specificity for polyps 10 mm, substantial portions of the screening population will need colonoscopy with each pass of CTC. With these low positive predictive values, many patients and their doctors will want repeat CTC to determine if a lesion is actually present when one cannot be found during colonoscopy. The test probably has adequate performance for patients who refuse to use bowel preparation for colonoscopy, but patients should be warned about the substantial chance of a false-positive result that will require colonoscopy anyway, the need to repeat the test in 5 years rather than 10 years even if the test is negative, and the persisting concerns about radiation risk and incidental extracolonic findings.

—  K. Rex, MDPublished in Journal Watch Gastroenterology May 18, 2012

Citation(s):Zalis ME et al. Diagnostic accuracy of laxative-free computed tomographic colonography for detection of adenomatous polyps in asymptomatic adults: A prospective evaluation. Ann Intern Med 2012 May 15; 156:692.

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[Guest guest]

"Laxative-Free CT Colonography: Still Not Good Enough"The last one I had a prep that was so benign that I do not really understand the fuss.Haven't most of us cleaned out below to have something stuck up there often enough that this should just not be an issue?JB

[Guest guest]

"Laxative-Free CT Colonography: Still Not Good Enough"The last one I had a prep that was so benign that I do not really understand the fuss.Haven't most of us cleaned out below to have something stuck up there often enough that this should just not be an issue?JB

[Guest guest]

Do you think the prep harms one's microbiome? From: J Barrowster <barrowster@...> Sent: Saturday, May 19, 2012 9:07 AM Subject: Re:

Laxative-Free CT Colonography: Still Not Good Enough

"Laxative-Free CT Colonography: Still Not Good Enough"The last one I had a prep that was so benign that I do not really understand the fuss.Haven't most of us cleaned out below to have something stuck up there often enough that this should just not be an

issue?JB

[Guest guest]

Do you think the prep harms one's microbiome? From: J Barrowster <barrowster@...> Sent: Saturday, May 19, 2012 9:07 AM Subject: Re:

Laxative-Free CT Colonography: Still Not Good Enough

"Laxative-Free CT Colonography: Still Not Good Enough"The last one I had a prep that was so benign that I do not really understand the fuss.Haven't most of us cleaned out below to have something stuck up there often enough that this should just not be an

issue?JB