Common Procedures > Faecal Occult Blood Test
What is it?
The faecal occult blood test (FOBT) checks for evidence of microscopic blood in stools.
What is the purpose of it, and should I undertake it?
FOBT is used as a screening test for colorectal cancer. When combined with colonoscopy after a positive test, it has been shown to enable early identification of asymptomatic colorectal cancer, asymptomatic pre-cancerous polyps, and ultimately reduce colorectal cancer mortality.
It is recommended for asymptomatic individuals at average-risk of developing colorectal cancer. These would be individuals who:
FOBT is NOT recommended for individuals who are at increased risk of colorectal cancer, or have alarm symptoms such as change of bowel habits, visible per rectal bleeding (on the stools or on toilet paper), have a personal history of colorectal cancer or polyps, a medical condition or family history predisposing them to colorectal cancer. These individuals should be referred for specialist evaluation and considered for colonoscopy upfront.
What does it involve?
Collection of a small amount of naturally passed stool is required. It is generally a simple procedure that can be done at home. The collection kit and method of returning the samples may vary depending on the healthcare provider.
There are two types of FOBT – the guaiac-based faecal occult blood test (gFOBT) and the faecal immunochemical test (FIT).
The older guaiac-based method (gFOBT) method requires samples from 3 stool specimens on separate days, as well as certain dietary and medication precautions to minimise false positive or false negative results.
Most current providers use the immunochemical method (FIT) which only requires samples from 2 specimens on separate days, and do not require specific dietary or medication precautions.
What do the results mean, and what follow up is needed?
A positive FOBT/FIT predicts an increased risk of having colorectal cancer or pre-cancer polyps. This warrants further evaluation with colonoscopy. Whilst the majority of individuals who undergo colonoscopy for positive FOBT/FIT do not have colorectal cancer – for those who do, early detection can improve the chances of cure and reduce mortality. Pre-cancerous colorectal polyps can also be identified and be removed during a colonoscopy, minimising future risk of cancer transformation.
A negative FOBT/FIT – whilst less concerning than a positive result – does not completely exclude colorectal polyps or cancer. Ongoing annual FOBT/FIT screening is recommended.
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