CMS Sets Different Standards For CT Colonography?

n the February 2010 edition of the Annals of Internal Medicine, Samita Garg, MD; and Dennis J. Ahnen, MD discuss at length about the decision of the Centers for Medicare & Medicaid Services (CMS) to not cover computed tomographic colonography (CTC) screening for colon cancer.

The rationale for the CMS decision includes concerns about radiation exposure, miss rates for small polyps, detection of incidental extracolonic findings, variability in performance, and lack of evidence that adding computed tomographic colonography would increase overall screening rates. The authors discusses about these concerns and point out that these concerns are associated with other recommended and covered screening tests as well, and some where set only for CTC.

Radiation Exposure

Radiation exposure fron CTC is low (about 6-8 mSv per examination) and the cancer risk estimated is unclear. But Barium enema, which exposes to similar radiation dose is covered by the CMS for colon cancer screening.

False Negative Rates for Polyps

Even though studies have proven that CTC is less sensitive in detecting small polyps (≤5 mm in diameter) when compared to colonoscopy, the benefits of detection, removal and follow-up pof small polyps is uncertain. CMS accepted tests colonoscopy misses up to 25% of small polyps and 12% of polyps larger than 1 cm, sigmoidoscopy cannot see proximal colon while faecal colonoscopy misses almost all small polyps.

Extracolonic Findings

Seven to 16% of CTC detect extracolonic abnormalities leading to further testing, overdiagnosis, and overtreatment.

The USPSTF (2) concludes that "the evidence to assess the harms related to extra-colonic finding is insufficient, and the balance of benefits and harms cannot be determined."

A recent large study (19) reported that only 12% of 1169 patients who underwent upper endoscopy after negative results on colonoscopy that was performed because of positive results on fecal occult blood testing had a significant finding (such as arteriovenous malformation, ulcers, suspected Barrett esophagus, or esophageal stricture), and whether identification of these lesions is ultimately beneficial or harmful remains uncertain.

Variability in the Reliability of CTC

While it was pointed out that CTC is less reliable due to the variability in the results, the quality of colonoscopy in the United States varies greatly is also well established. Detection rates of serious adenomas (those larger than 1 cm in diameter) vary up to 4-fold (20). Also, colonoscopy complications vary by more than 10-fold.

Lack of Targeted Studies

Studies of CTC have not specifically targeted patients aged 65 years or older who are eligible for Medicare, but participants 65 years or older were included in the large CTC studies (8-10). But targeted studies of the other colorectal cancer screening tests in patients 65 years or older have also not been reported.

Higher Adenoma Prevalence

More adenomas in above 65yrs leads to higher follow-up colonoscopies but sigmoidoscopy can also lead to this.

Overall Adherence

The CMS argual that adding CTC to colorectal screening options may increase the number of participants who would accept screening is unproven seems to be a totally new standard that only CTC is expected to meet.

Cost efectiveness

Cost-effectiveness modeling seems to be part of a new and higher standard that may be applied to future colorectal cancer screening tests.

Finally the authors concludes that CTC is being held to a higher standard than the other colorectal cancer screening tests (like colonoscopy, sigmoidoscopy, faecal occult blood examination, Barium enema etc) that are currently recommended by the USPSTF and covered by the CMS.