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Reference: Gut 2015 Feb;64(2):272 (level 2 [mid-level] evidence)
Colon cancer screening is recommended beginning at age 50 years for adults with an average risk of cancer and optical colonoscopy is the standard screening method (Gastroenterology 2008 May;134(5):1570). Colonoscopy is associated with reduced risk of colon cancer and colon cancer-related mortality (Ann Intern Med 2011 Jan 4;154(1):22, BMJ 2014 Apr 9;348:g2467), but incomplete colonoscopy may significantly increase the risk of missed polyps and adenomas (Colorectal Dis 2015 Jan 21 early online, BMC Gastroenterol 2014 Mar 29;14:56). Two methods of follow-up after incomplete colonoscopy include colon capsule endoscopy and computed tomography (CT) colonography. While both procedures do not require sedation, CT colonography requires air insufflation and also exposes the patient to low-dose radiation, which is associated with a small, but significant, increase in the risk of cancer (Gastrointest Endosc Clin N Am 2010 Apr;20(2):279, Eur J Radiol 2013 Aug;82(8):1159). A recent diagnostic cohort study compared the ability of colon capsule endoscopy and CT colonography to identify polyps at least 6 mm in size in 100 patients (median age 59 years and 66% female) with prior incomplete colonoscopy. The reasons for incomplete colonoscopy included excessive pain in 45%, difficult examination in 38%, and tortuosity of the colon in 17%.
Patients had colon capsule endoscopy followed by CT colonography on the same day and outcome assessors were blinded to the results of the other test. If a polyp or mass at least 6 mm in size was detected on either test, the patient underwent repeat colonoscopy within 1 month. If both tests were negative, however, patients did not receive a repeat colonoscopy and were assessed for missed cancers by clinical follow-up at 1 year. Colon capsule endoscopy detected polyps at least 6 mm in size in 25 patients, with only 1 false positive result and no false negative results. CT colonography, on the other hand, only detected polyps at least 6 mm in size in 14 patients, with 2 false positive results and 12 false negative results. Taken together, the colon capsule endoscopy had a relative sensitivity of 2 (95% CI 1.34-2.98) compared to CT colonography. The remaining 74 patients with negative results on both tests reported no missed cancers during mean 20-month follow-up.
This study shows that colon capsule endoscopy may detect more polyps than CT colonography after an incomplete colonoscopy. The absolute diagnostic accuracy of these tests, however, could not be determined in this study. Patients with negative results on both tests did not have a follow-up colonoscopy and therefore a true false negative rate could not be determined due to the possibility that a patient could have had a false negative result on both tests. The follow-up period was insufficient to clinically rule out a missed cancer and equally important, a missed polyp (a key point of the screening being to detect precancerous lesions). Further studies with longer follow-up durations are necessary to determine the proper management after a negative evaluation with either colon capsule endoscopy or CT colonography.
For more information, see the Colonoscopy and Virtual colonoscopy topics in DynaMed.