Faecal Occult Blood Test (FOBT)

This is one of the simplest screening tests and is based on the fact that colorectal polyps and cancers can bleed into the colon.  The amount of bleeding can be very small and not visible (hence occult).  It can be detected by special tests on the faeces. 

The test is available in a kit with instructions.  The person takes it home and follows the instructions to sample the stools for occult blood (OB).  If OB is present, he/she has to undergo further investigations such as colonoscopy or barium enema to exclude a polyp or cancer.  This is because OB can be also due to piles, colitis or other non-cancerous conditions.

Conversely if OB is absent, it does not mean that a person is entirely free of colorectal polyp or cancer as the test is not 100% accurate e.g. eating partially cooked meat or certain foods can affect the test and cause a false positive result.

However, with newer methods for detecting OB, FOBT is now more accurate and recent research has shown that it can detect colorectal polyps and early colorectal cancers.

The Singapore Cancer Society distributes free FOBT kits to Singaporeans and Permanent Residents who are 50 years old and above. Please see Cancer Screening – FOBT page for more details.

Digital Rectal Examination

This is routinely performed by the physician during clinical examination.  As the finger can only reach the anus and lower rectum, it can only detect 10% of CRC.

Flexible Sigmoidoscopy or Colonoscopy

This test involves the examination of the colon & rectum using a flexible fiber optic instrument introduced in the anus. The patient is under sedation and can experience abdominal discomfort. When the examination is limited to the sigmoid colon (left colon) it is called sigmoidoscopy and if it involves the whole colon it is called colonoscopy.  In addition to its diagnostic use, the colonoscopy can be used for treatment e.g. remove polyps, biopsy cancerous lumps, inject bleeding spots.  Colonoscopy is a safe procedure with a low incidence of complications.

Double Contrast Barium Enema X-ray

This is a special x-ray examination of the colon & rectum and its accuracy is equivalent to that of colonoscopy.  The disadvantage is that if a polyp or a cancer is detected, a colonoscopy is needed to biopsy it.  Its advantages over the colonoscopy are 1) less expensive 2) better at locating the polyp or cancer 3) less complications.

Screening Recommendations

Beginning at age 45 to 50 years

• Have a faecal occult blood test yearly
• Have a sigmoidoscopy every 5 years
• Or a colonoscopy every 10 years
• Or a barium enema x-ray every 10 years
• A digital rectal examination is performed every 5 to 10 years

Those in the high risk group should have screening earlier and/or more frequently. Polyps found on screening should be removed to prevent the transformation to CRC.