Faecal Occult Blood

What is the Faecal Occult Blood Test?

Faecal occult blood (FOB) refers to blood in the stool that is not visible to the naked eye. The test (FOBT) checks for this blood via a stool sample. The new test used as part of the National Bowel Cancer Screening Program (NBCSP) is an immunochemical test (iFOBT) that uses specific antibodies to detect globin.

Why should I do FOBT?

FOBT is a way to detect blood in the stool in the proportion of the population who do not have symptoms. This may be an indication of a significant polyp or even a cancer. Approximately 7% of patients tested will have a positive FOBT.

I have a positive FOBT. Do I have bowel cancer?

In Australia, only 1 in 33 patients with a positive FOBT will have a bowel cancer (3%). The rationale for screening is that it will detect the cancer when it is early before it has caused symptoms. There is also a rate of polyps of around 40% of patients with a positive FOBT. That means that nearly 60% of patients with a positive FOBT will have a completely normal colonoscopy.

When should I do FOBT?

An FOBT is recommended for all Australians at average risk of bowel cancer from the age of 50 every 2 years. That is of course unless you have a strong family history, underlying genetic abnormality or other reason for colonoscopy such as symptoms like rectal bleeding or a history of inflammatory bowel disease.

What is the evidence?

Bowel cancer can be treated successfully in the early stages. It is estimated that screening with FOBT will decrease the risk of death by colorectal cancer by 15-25%.