Wednesday, 26 April 2017

CT colonography

CTC is a potential technique for CRC screening. With CTC, two- and three-dimensional digital images are constructed to investigate the presence of lesions in the colon and rectum. Studies on the impact of CTC screening on CRC incidence or mortality have not yet been conducted. Seven systematic reviews have been published between 2003 and 2008 on CTC performance characteristics in comparison to colonoscopy (Sosna et al. 2003; Halligan et al. 2005; Mulhall, Veerappan & Jackson 2005; Purkayastha et al. 2007; Rosman & Korsten 2007; Walleser et al. 2007; Whitlock et al. 2008). All metaanalyses and primary studies (Reuterskiold et al. 2006; Arnesen et al. 2007; Chaparro Sanchez et al. 2007) reported that sensitivity was low for small polyps and increased with polyp size. The incidence of adverse events was very low in all studies which assessed this outcome. Three studies also reported patient preferences and found that participants prefer CT colonography over colonoscopy, (Jensch et al. 2008; Roberts-Thomson et al. 2008). None of the retrieved studies considered the possible damage associated with radiation. All studies concluded that CT is not ready for routine use in clinical practice.

Before CTC can be recommended for average-risk screening, it must be demonstrated to be highly and consistently sensitive in a variety of settings and questions about the optimal technological characteristics of the technique must be settled. These questions include the appropriate threshold size for referral of findings, costs of the procedure in relation to its effectiveness and the potential risks from the radiation exposure  

Stool DNA 

With stool DNA testing, faeces are investigated for the presence of disrupted or methylated DNA. There have been no studies evaluating the CRC incidence or mortality reduction from stool DNA testing. Systematic reviews of performance characteristics of stool DNA tests (Bluecross Blueshield Association Special Report: 2006; Whitlock et al. 2008; Loganayagam 2008) included two prospective studies assessing diagnostic performance in an average-risk population (Imperiale et al. 2004; Ahlquist et al. 2005). Both studies found that stool DNA testing was more sensitive than Hemoccult II for advanced neoplasia, without loss of specificity. However, sensitivity of stool DNA was still only 50% and 20% in the respective studies

A new version of the stool DNA test has been developed that incorporates only two markers. The use of only two markers will make the test easier to perform, reduce the cost, and facilitate distribution to local laboratories. In a case–control study of this test, Itzkowitz found a high sensitivity of 83% but the specificity was significantly worse than the older version at 82%

An important issue which must be addressed before widespread implementation of stool DNA testing becomes possible involves costs. Two studies have shown that at current costs of approximately US$ 350, stool DNA screening is not a cost-effective option for CRC screening (Zauber et al. 2007; Parekh, Fendrick & Ladabaum 2008). According to one study, costs should be 6–10 times lower before stool DNA screening could compete with other available screening tests 

Stool DNA with version 1 testing has superior sensitivity over Hemoccult II, at similar levels of specificity (III). Version 2 seems to have even better sensitivity, at the expense of worse specificity (IV). The diagnostic accuracy of stool DNA needs to be confirmed by large multicentre prospective trials in the average-risk population, and costs need to be reduced before stool DNA testing can be recommended for CRC screening  

Capsule endoscopy 

With capsule endoscopy, a camera with the size and shape of a pill is swallowed to visualise the gastrointestinal tract. No studies have reported on CRC incidence and mortality reduction from capsule endoscopy. Two reviews have evaluated its test performance characteristics compared to colonoscopy and/or CT colonography (Fireman & Kopelman 2007; Tran 2007). Since the reviews, four more studies on the diagnostic accuracy of capsule endoscopy have been published (Eliakim et al. 2009; Gay et al. 2009; Sieg, Friedrich & Sieg 2009; Van Gossum et al. 2009). Sensitivity in the studies included in the review varied from 56–76%, and specificity from 64–69% (Fireman & Kopelman 2007; Tran 2007). The newer studies showed somewhat better estimates than the earlier studies, with sensitivity ranging from 72–78% and specificity from 53–78% (Eliakim et al. 2009; Gay et al. 2009; Sieg, Friedrich & Sieg 2009; Van Gossum et al. 2009). However, these test characteristics are still inferior compared to colonoscopy.

Capsule endoscopy bears promise as an alternative to colonoscopy, because the examination can be realised without intubation, insufflation, pain, sedation or radiation; no serious adverse effects have been reported. However, accuracy data show inferior performance compared to colonoscopy (III). Better diagnostic performance results from large multicentre prospective trials in the average-risk population are required before capsule endoscopy can be recommended for screening 

No comments:

Post a Comment

Popular Posts