Screening Tests To Help Guard Against Colorectal Cancer

March 3, 2020

Colorectal cancer is the most common cancer in Singapore, with about 20 persons out of 100,000 getting diagnosed with it every year. The good news is, colorectal cancer is treatable, especially if detected early.

A crucial step in guarding against colorectal cancer is regular screenings. This increases the likelihood of discovering pre-cancerous or cancerous growths, and increases the success rate of treatment methods.

But speaking of screenings for colorectal cancer, do you know what they are? In fact, there are quite a few tests available for rectal and colon cancer in Singapore, but each comes with their pros and cons. Take a look at some of them below.


Colonoscopy has long been regarded as the golden standard for polyp detection. It involves the insertion of a long, thin, flexible tube with an attached camera into the rectum to assess the large intestine. Colonoscopy has a high detection accuracy, and can examine the whole length of the colon. During the procedure, small polyps can also be removed, or biopsies performed.

The recommended frequency for a person of average risk is once every 10 years. For people at higher risk, or those who have polyps before, the recommended frequency may increase as advised by their doctor.


A full bowel preparation is necessary before the procedure, and sedation is required during the process. Taken together, the prep, process, and recovery time may take up to a whole day or more. With colonoscopy, there is also a small risk of bleeding and perforation of the intestinal walls.

Faecal occult blood test (FOBT) / Faecal immunochemical test (FIT)

These are tests which detect blood in the stools. The stool samples can be collected at home before being sent to the doctor’s lab for testing. There is little risk as there is no direct contact with the body involved. The recommended frequency for FOBT/FIT as colorectal screening is once a year.


The detection abilities of FOBT and FIT are not as robust as colonoscopy, as not all cases of cancer result in bleeding – and not all bleeding means cancer. Upon finding positive (abnormal) results, a colonoscopy is still usually needed to confirm the presence of polyps or cancer.


Similar to a colonoscopy, a thin, flexible scope is used to view the rectum and colon. With sigmoidoscopy, only the lower colon can be examined. A biopsy or removal of polyps can be performed during the procedure, which usually does not require sedation. Bowel prep is needed, but this is less intensive than what is necessary before a colonoscopy.

For people at average risk who choose to do sigmoidoscopy as a routine screening test, the recommended frequency is once every 5 years.


Sigmoidoscopy does not examine the entire length of the colon, so it could miss polyps that are further up the large intestine. As with colonoscopy, there is also a small risk of bowel perforation.

Virtual colonoscopy / CT colonography

CT colonography uses computed tomography (CT) to examine the colon and rectum. A tube is inserted at the opening of the rectum to inflate the bowel with air to aid in visualisation. CT colonography allows examination of the entire bowel to detect polyps and cancer, without the risk of causing injuries to the bowel. No sedation is required.


Full bowel preparation is necessary before the procedure. Studies show that CT colonography is slightly inferior to colonoscopy at detecting cancer, and is even less reliable when it comes to finding smaller polyps. In the case of abnormalities detected, a follow-up colonoscopy will need to be performed for further exploration or removal of polyps.


The reliable detection abilities of colonoscopy make it, by far, one of the most reliable methods for detecting colorectal cancer. But due to its more invasive nature, risks present, and inconveniences to the patient, some may prefer other screening methods like the low-risk and cost-effective FOBT/FIT, or the less-invasive CT colonography.

The screening test best suited for you should consider your preferences as well as your doctor’s recommendation. If you detect any abnormalities in your bowel health, are above the age of 50, or have a high risk of developing colorectal cancer, do speak a colon cancer specialist about when you should start regular colorectal cancer screening.