More recently, non-invasive virtual colonoscopy is possible using various radiological modalities that construct a 3D 'virtual' image of the colon. In CT colonography, multi-slice spiral computed tomography (CT) technology allows sufficiently rapid capture of data to compensate for artefact from bowel movement. 'Virtual' colonoscopy can also refer to MR colonography
- Investigation of lower GI symptoms, including:
- Altered bowel habit
- Exclusion of colorectal cancer in symptomatic patients.
- Colorectal cancer surveillance
- Assessment of inflammatory bowel disease
Sensitivity and Specificity
The sensitivity of a test depends on the disease or condition in question and also the gold standard it is being compared against. For most conditions, colonoscopy is regarded as the gold standard investigation with a theoretical sensitivity of 100%. In conditions like inflammatory bowel disease, direct inspection of the mucosa is essential and the added ability to biopsy the mucosa gives information not obtainable from non-invasive imaging.
In practice, however, the 'sensitivity' of colonoscopy is not 100%. The diagnostic yield is influenced by several factors including equipment, operator factors, the quality of bowel preparation and the conditions studied.
Using colorectal polyps as a disease, an idea of the true 'sensitivity' of colonoscopy has been estimated by using back-to-back colonoscopy, or by comparing it to newer modalities like CT colonography (see  and CT colonography page).
Risks and Consent
- Perforation 1:1000 (about 2:1000 if polypectomy)
- Bleeding, especially if biopsy performed.(about 2:1000 exams without biopsy).
- Other risks are rare and include:
As the majority of colonoscopies are performed as day-cases, the BSG has produced consent forms and booklets that can be sent out to the patients in advance of the procedure. This has the advantage of speeding up the running of the endoscopy unit, but is also good practice as it avoids the less than ideal situation of signing consent forms in the procedure room, minutes before the endoscopy itself. The total risk of complications with morbidity is 0.2%. 
Role of Prophylactic Antibiotics
Antibiotics may reduce bacteraemia, but it is unclear if this reduction has any clinical significance. Some practitioners use antibiotics if there are heart valve lesions thought to predispose to bacterial endocarditis and sometimes if the patient has an orthopaedic prosthesis.
See also Bacterial Endocarditis:Prophylaxis
Some patients prefer sedation, though it is not a strict requirement. In a small number of cases, where significant discomfort is anticipated, the procedure can be performed under general anaesthesia. However, over-sedation can be a dangerous thing as an almost unconscious patient may not respond to discomfort with the normal cues.
The patient is placed in the left lateral position. Prior to starting the procedure, a digital rectal examination is performed. This allows examination of the peri-anal region and is also useful excluding low rectal tumours that can sometimes be missed by the colonoscope.
The entire length of the large bowel is examined both on entry and withdrawal of the scope. A complete colonoscopy should reach the caecum and this can be confirmed by several methods. Intubation of the terminal ileum is the only sure indication of having reached the caecum, but other surrogate methods include transillumination of the abdominal wall, palpation of the right iliac fossa, and, identification of the tri-radiate fold or appendiceal orifice.
Training and Quality Issues
The introduction of faecal occult blood testing for colorectal cancer screening in the UK prompted an accreditation scheme to ensure a minimum standard of operator competence. A national audit in the UK, shortly before the introduction of the programme was disappointing.
The completion rates of colonoscopy are operator dependent. An accrediation scheme exists for any endoscopist wanting to participate in the UK colorectal cancer screening programme. These stipulate that the operator:
- Should have performed >1000 before entering the scheme.
- Perform >150 annually
- Should achieve caecal intubation in >90% of cases (unadjusted for case-mix).
Joint Advisory Group on Gastrointestinal Endoscopy (JAG) set out training standards. Training should be carried out only in JAG accredited centres.
Before trainees can be 'signed off', they should be expected to:
- Perform ~100 procedures a year
- Achieve caecal intubation in >90% of cases (unadjusted for case-mix).
A minimum of 200 is thought to be necessary to acquire competence.
Several enhancements and adjuncts can further improve the utility of colonoscopy.
The use of dyes such to allow characterisation and identification of lesions that appear equivocal or are difficult to see on standard optical endoscopy, e.g. flat adenomas or dysplastic regions in long-term inflammatory bowel disease. The appearance of the lesion in chromoendoscopy can be used to decide if it is suitable for endoscopic mucosal resection.
Dyes include indigo carmine, methylene blue, crystal violet and acetic acid. They work either on the principle of contrast or staining (due to absorption or reaction). Contrast dyes, e.g. indigo carmine and acetic acid, pool in the grooves and uneven contours of the lesion, accentuating abnormal surface texture. This can be washed away in contrast to staining dyes which actually stain the cells and can take some minutes to work.
Use of smaller section of the light spectrum accomplished through the use of light filters. The narrower spectrum accentuates smaller, more superficial blood vessels. Normal mucosa appears blue-green, stool appears red and blood and vascular structures appear black. NBI can be toggled on and off during colonoscopy allowing easy switching betwee NBI and conventional views.
NBI allows assessment of pit pattern and vascular pattern intensity which permits more accurate characterisation of lesions. In can be particularly helpful in identifying subtle lesions such as flat adenomas or, in the case of patients with colitis, it allows better identification of DALMs.
Confocal Chromoscopic Endomicroscopy
Combination of dyes and confocal microscopy techniques allow real-time microscopic examination of deeper mucosal layers.
- ↑ Rex DK, Cutler CS, Lemmel GT, Rahmani EY, Clark DW, Helper DJ, Lehman GA, Mark DG. Colonoscopic miss rates of adenomas determined by back-to-back colonoscopies. Gastroenterology. 1997 Jan;112(1):24-8.
- ↑ Bressler B, Paszat LF, Vinden C, Li C, He J, Rabeneck L. Colonoscopic miss rates for right-sided colon cancer: a population-based analysis. Gastroenterology. 2004 Aug;127(2):452-6.
- ↑ Cotton PB, Durkalski VL, Pineau BC, Palesch YY, Mauldin PD, Hoffman B, et al. Computed tomographic colonography (virtual colonoscopy): a multicenter comparison with standard colonoscopy for detection of colorectal neoplasia. JAMA : the journal of the American Medical Association 2004;291:1713-9. (Direct link – subscription may be required.)
- ↑ Levin TR, Zhao W, Conell C, Seeff LC, Manninen DL, Shapiro JA, et al. Complications of colonoscopy in an integrated health care delivery system. Annals of internal medicine 2006;145(12):880-6.
- ↑ Dunlop MG; British Society for Gastroenterology; Association of Coloproctology for Great Britain and Ireland. Guidance on large bowel surveillance for people with two first degree relatives with colorectal cancer or one first degree relative diagnosed with colorectal cancer under 45 years. Gut. 2002 Oct;51 Suppl 5:V17-20. Direct link: http://gut.bmjjournals.com/cgi/content/full/51/suppl_5/v17
- ↑ Ko CW, Riffle S, Michaels L, Morris C, Holub J, Shapiro JA, Ciol MA, Kimmey MB, Seeff LC, Lieberman D. Serious complications within 30 days of screening and surveillance colonoscopy are uncommon. Clinical gastroenterology and hepatology : the official clinical practice journal of the American Gastroenterological Association. 2010 Feb; 8(2):166-73.(Link to article – subscription may be required.)
- ↑ Bachir NM, Feagins LA. Postcolonoscopy appendicitis in a patient with active ulcerative colitis. World journal of gastrointestinal endoscopy. 2010 Jun 16; 2(6):232-4.(Link to article – subscription may be required.)
- ↑ BSG 2006 Colonoscopy Booklet (pdf)
- ↑ BSG 2006 Colonoscopy Booklet with Consent Form (pdf)
- ↑ Article on Antibiotic Prophylaxis. (part of AGA Gastroenterology & Hepatology Annual Review 2006)
- ↑ European Society of GI Endoscopy Guidelines on Prophylactic Antibiotics
- ↑ Hirota WK, Petersen K, Baron TH, Goldstein JL, Jacobson BC, Leighton JA, Mallery JS, Waring JP, Fanelli RD, Wheeler-Harbough J, Faigel DO; Standards of Practice Committee of the American Society for Gastrointestinal Endoscopy. Guidelines for antibiotic prophylaxis for GI endoscopy. Gastrointest Endosc. 2003 Oct;58(4):475-82. Review.
- ↑ Canadian Society of Colon and Rectal Surgeons Practice Guidelines on Prophylactic Antibiotics
- ↑ Bowles CJA, Leicester R, Swarbrick E, Williams CB, Romaya C, Epstein O. Intercollegiate-BSG national colonoscopy (IBNC) audit: methods used to identify the caecum and caecal intubation rate. Gut 2001;48(suppl I): A10, #36
- ↑ BMJ 2004 Rapid Response
- ↑ Bowles CJ, Leicester R, Romaya C, Swarbrick E, Williams CB, Epstein O. A prospective study of colonoscopy practice in the UK today: are we adequately prepared for national colorectal cancer screening tomorrow? Gut 2004;53(2):277-83.
- ↑ Atkin W, Rogers P, Cardwell C, Cook C, Cuzick J, Wardle J, et al. Wide variation in adenoma detection rates at screening flexible sigmoidoscopy. Gastroenterology 2004;126(5):1247-56.
- ↑ NCEPOD 2004 Scoping Our Practice Report
- ↑ Kudo S, Kashida H, Tamura T, Kogure E, Imai Y, Yamano H, et al. Colonoscopic diagnosis and management of nonpolypoid early colorectal cancer. World journal of surgery 2000;24(9):1081-90.
- ↑ Hurlstone DP, Sanders DS, McAlindon ME, Thomson M, Cross SS. High-magnification chromoscopic colonoscopy in ulcerative colitis: a valid tool for in vivo optical biopsy and assessment of disease extent. Endoscopy 2006;38(12):1213-7. (Direct link – subscription may be required.) One author of this work has subsequently resigned from his position and as of October 2009 is under going a Fitness to Practise Hearing by the GMC
- ↑ Hurlstone DP, Sanders DS, Thomson M. Detection and treatment of early flat and depressed colorectal cancer using high-magnification chromoscopic colonoscopy: a change in paradigm for Western endoscopists? Digestive diseases and sciences 2007;52(6):1387-93. (Direct link – subscription may be required.) One author of this work has subsequently resigned from his position and as of October 2009 is under going a Fitness to Practise Hearing by the GMC
- ↑ Hata K, Watanabe T, Shinozaki M, Kojima T, Nagawa H. To dye or not to dye? That is beyond question! Optimising surveillance colonoscopy is indispensable for detecting dysplasia in ulcerative colitis. Gut. 2004 Nov; 53(11):1722.
- ↑ Machida H, Sano Y, Hamamoto Y, Muto M, Kozu T, Tajiri H, et al. Narrow-band imaging in the diagnosis of colorectal mucosal lesions: a pilot study. Endoscopy 2004;36(12):1094-8. (Direct link – subscription may be required.)