Types of Colon Cancer Screening in Singapore

The three main ways to examine the colon are: colonoscopy, barium enema and computer tomography (CT) colonography (aka virtual colonoscopy). All three methods require the patient to clear their bowels beforehand so that the doctor can obtain a clear view of the entire length of the colon.

The most accurate, common and recommended form of colon screening is a colonoscopy, as it not only allows for clear visualization of the colon, it also allows the doctor to obtain tissue samples for biopsies and remove abnormal growths on the spot.

1. Colonoscopy

Colonoscopy is regarded as the ideal standard for colon cancer screening. A small, flexible tube containing a light and camera is inserted through the anus, and advanced all the way through the colon. This gives the doctor high quality and real-time images of the inside of the colon.

Should any abnormal growths be found, they can be removed on the spot or taken for a biopsy, which will determine with certainty if it is cancerous or not.

This procedure is usually performed under sedation, so it is painless. After the procedure, you may only feel minor discomfort such as bloating. A rare complication is perforation of the colon wall, but it is very unlikely in the hands of an experienced colorectal surgeon.

Learn more about this diagnostic technology, in Dr Ho Kok Sun's dedicated website: Colonoscopy Clinic Singapore.

2. Barium Enema

The barium enema method involves the insertion of a tube into the anus, through which a bag of white liquid (barium) will be poured in. The patient will then be rotated so that the barium can flow through the entire length of the colon. After this is done, the barium will be drained back out. Air will then be pumped in through the tube so as to inflate the colon (providing a clearer view), and x-ray images will be taken with the patient in different positions.

3. CT Colonography (Virtual Colonoscopy)

Here, a tube will be inserted through the anus and 1 to 1.5 liters of air will be pumped in to inflate the colon. The patient will then lie on his back in the CT scanner, given an intravenous injection and the scan will be performed. The patient will then lie on his stomach and the same process is repeated. The virtual image of the colon will then be generated.

Comparing the 3 Screening Methods

Barium enema nowadays is near obsolete and have been replaced by CT colonography. The main advantage of CT colonography over colonoscopy is that the perforation rate is lower (0.05% versus 0.10% for colonoscopy). Some patients also worry about the “perceived” invasiveness of having a tube go into the colon.

CT colonoscopy is not performed under sedation, so most will feel some bloating/discomfort when the air is pumped in. There is also radiation involved, as well as an injection of intravenous contrast, which has a minor risk of kidney injury. Accuracy of CT colonography is also slightly lower than colonoscopy.

The most important difference is that CT colonography can only diagnose and pick up polyps and cancers, but would still need a colonoscopy to remove the polyps or to biopsy any suspicious area to test for cancer.

BLOOD TESTS

  • Carcino-Embryonic Antigen (CEA)
    This is a blood test that is commonly used to screen for colon cancer. Unfortunately, it only has a sensitivity level of about 70%. This means that 30% of cancer patients might have a normal CEA level; and besides, not all people with high CEA levels necessarily have cancer.

    As such, this is not a definitive test for colon cancer, and is no longer recommended as a test for screening for colon cancer. However, some still prefers to check their CEA for the lack of other alternative blood tests.
  • Stool Occult Blood Test
    This test is used to detect the presence of blood in stools – blood not visible to the naked eye. This involves taking a stool sample and sending it for testing within 48 hours. This blood test is based on the assumption that as stool passes a large polyp or cancer, it will bleed and the stool will be mixed with blood not visible to the naked eye.

    Depending on the type of test used to analyze the stools for blood, the accuracy level is between 70-85%. This means that for every 100 patients with confirmed colorectal cancer, 15-30 of them actually have a negative stool test. Furthermore, some older tests can be inconvenient and require one to abstain from meat and other food for a few days before the test. Improper storage or any delay in processing the stool sample will also affect accuracy levels.

    However, in spite of its limitations, this serves as a suitable population-wide general screening tool due to its affordability and convenience. However, it is certainly not a conclusive test for colon cancer; it simply indicates a warning sign for one to go for a more detailed colon screening.
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