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All the different tests to examine the colon requires proper cleansing of the colon. There are 3 different ways to examine the colon: colonoscopy, barium enema and computer tomography (CT) colonography (also known as virtual colonoscopy).


Colonoscopy is the gold standard for examination of the colon. This entails inserting a flexible tube through the anus and advancing it up along the rectum and colon until it reaches the beginning.

Colonoscopy is usually done under sedation though some patients opt to be awake and watch the entire proceeding. The major advantage of colonoscopy is that it is not just a diagnostic procedure, but it also allows for removal of polyps and to take tissue samples for testing.

Most people are fearful of colonoscopy because they feel that it is a very invasive procedure and are concerned about pain. Most patients do not feel any pain or even remember about the procedure after the they wake up from sedation. The most feared complication that may occur is that of perforation where the scope results in damage and a break in the colon wall. If that happens, colorectal surgery is usually required to rectify it. The risk is usually less than 0.1%.

A colonoscopy is the ideal way of screening for colorectal cancer, due to its high levels of safety, accuracy, clarity, comfort and convenience.

Barium Enema

Barium enema is another way to examine the colon. This is performed by a radiologist who first inserts a tube through the anus. A bag of white liquid (barium) is then poured into the colon through the tube. The patient is rotated so that the barium can flow around the colon. The bag is then dropped to the floor and the barium allowed to flow out. Air is then pumped in through the tube to distend the colon and x-ray images are taken with the patient in different positions.

There is no sedation given for barium enema.

CT Colonography (also known as Virtual Colonoscopy)

The latest available technique to examine the colon is CT colonography or virtual colonoscopy. The patient also has to have bowel preparation. At the time of the investigation, the radiologist will insert a tube into the rectum via the anus. One to 1.5 litres of air will be pumped in to inflate and distend the colon. The patient will lie down on his back in the CT scanner, an intravenous injection given and the scan will be done. The patient will then lie prone on his tummy and the process repeated. The virtual image of the colon is then produced using computer software.

Colonoscopy Barium enema CT colonography
Advantages Accuracy- highest, especially for smaller polyps Lower perforation risk Lower perforation risk
Disadvantages Perceived invasive test Perforation risk 0.1% Least accurate
No biopsy
Perforation risk 0.04%
Accuracy in between barium enema and colonoscopy. Detection for polyps drop when size below 10mm Perforation risk 0.05 %
Sedation Available Not available Not available
Intervention Allows biopsy and removal of polyp No No
Speak to our experienced colorectal specialist for personalised advice on which screening method will be most suitable for your needs and preferences.

CEA (Carcino-Embryonic Antigen)

This is a blood test that is commonly used as part of health screening to screen for colon cancer. This test has a sensitivity and specificity of only about 70%. What this means is that it is abnormal in only 70% of patients, while 30% of cancer patients might have a normal CEA level, giving a false sense of security.

On the other hand, people with an abnormally high level of CEA does not mean that they definitely have colon or rectal cancer. It just means that they need further investigations. A high level of CEA could arise due to both cancerous conditions (cancer of colon, rectum, stomach, lung etc) and non-cancerous conditions such as smoking, lung infection, colon infection etc.

Stool occult blood test

Stool occult blood test is a test designed to detect presence of blood traces in the stools. This is to pick up blood that is otherwise not seen by the naked eye.

This test involves taking small sample to stools and sending it fresh (preferably within 48 hours).

The test is based on the assumption that if there any large polyps or cancer, it would bleed as the stools passes next to it. As this blood would have been mixed into the stools when it is passed out, it can no longer be seen with the naked eye. The accuracy depends on the different type of tests used to analyse the stools for blood and is in the region of 70-85%. Some of the older test requires abstinence from meat and other food for up to 3 days before the test and is very inconvenient. Unnecessary in delay or wrong storage of the stool sample prior to storage will also decrease the accuracy. What this means is that up to 30% of patients with colon and rectum cancer will have a negative result and be missed.

This test is more suited for population screening as it is cheaper and more convenient. This is not a diagnostic test for colon cancer. It is not for someone who already sees blood in the stools. It is just a warning indicator to go for a more complete examination of the colon.
Read on for More Information on Colorectal Cancer:
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Our Colorectal Cancer Surgeon
Ho Kok Sun Colorectal clinic logo
Dr Ho Kok Sun
Colorectal & General Surgeon
MBBS (Singapore),
M Med (Gen Surg) (Singapore),
FRCSEd (Gen Surg), FAMS
Dr Ho Kok Sun has been committed to treating colorectal cancer in Singapore for over a decade. He was the past President of the ASEAN Society of Colorectal Surgeons and the Society of Colorectal Surgeons (Singapore), as well as a founding member of the Eurasian Colorectal Technologies Association. Dr Ho was actively involved in the training of medical students and residents, and has published widely in reputable journals and book chapters. He believes that treatment should always be personalised to the patient’s needs.

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Ho Kok Sun Colorectal clinic logo
Ho Kok Sun Colorectal

Colorectal Surgeon

3 Mount Elizabeth,
Mount Elizabeth Medical Centre
#12-09, Singapore 228510

Tel (+65) 6737 2778
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