Persons 50 years of age without any family or personal history of colorectal, ovarian, or uterine cancer or of any other diseases known to increase risk of CRC, are considered to be at average risk. The Ministry of health Clinical Practice guidelines for Health screening makes the following recommendations for adults 50 years or older with average risk:
1. Fecal occult blood test annually plus sigmoidoscopy every 5 years or
2. Double-contrast barium enema every 5-10 years or
3. Colonoscopy every 10 years

There are 2 other groups of target population where screening can benefit:
a. those at Moderate Risk
b. those at High Risk of developing CRC (eg. family members with Familial Adenomatous Polyposis (FAP), immediate or close relatives of patients with CRC)

Those considered to be at moderate risk have a family (first-degree relative) or personal history of colorectal, ovarian, or uterine cancer. In the cases where there is a positive family history, it is recommended that screening should start 10 years earlier than the age of the first person diagnosed in family. Colonoscopy is recommended and should be repeated every 3-5 years. Those with a personal history of resected CRC should have a colonoscopy 1 year after surgery, then 3 years after surgery and subsequently once every 5 years, if findings are normal.

For high risk individuals, screening should start at least 10 years earlier than the youngest diagnosed case of FAP in the family and at 21 years for HNPCC. Colonoscopy is recommended and should be repeated every 1 to 2 years.

SCREENING TOOLS
a. Faecal occult blood testing (FOBT) – most widely used
b. Double-contrast barium enema (DCBE)
c. Flexible sigmoidoscopy/colonoscopy

FOBT is a test to check for blood in the stool. However, it is not completely accurate as dietary peroxidase from plant or meat products can give a positive result. Some drugs can also give a false negative result. Thus dietary restrictions are necessary to conduct this test. This kit is available in Singapore as the Haemoccult II®.

DCBE is cheaper and less invasive than a sigmoidoscopy or colonoscopy. It is a series of x-rays taken of the large intestines after a patient is given an enema of a white chalky solution to outline the colon on the x-rays. However, it is known to miss small lesions.

Flexible Sigmoidoscopy is an examination of the rectum and lower colon with a light source on a narrow flexible tube. It has been widely studied that 60-70% of CRC are left-sided and therefore within reach of the sigmoidoscope.

Colonoscopy is the gold standard in screening for the high-risk population. It uses a light source on a narrow flexible tube, a microscope and camera to view the rectum and entire colon. It also enables samples of tissue to be taken for testing. Its cost and complication rates have prevented it from a wider role in screening for the moderate risk population.

As we look to the future, newer tools are being developed for imaging of the gastrointestinal tract. These include virtual colonoscopy (also called CT colonography) and capsule endoscopy (where a patient swallows a minute electric capsule and periodic transmission of data allows clinical information to be collected; the capsule exits the body through normal bowel movement).