Faecal Occult Blood Test (FOBT / iFOBT)

Written by A/Prof Viraj Kariyawasam, Gastroenterologist

1. What is a Faecal Occult Blood Test (FOBT)?

A faecal occult blood test (FOBT), also known as an immunochemical faecal occult blood test (iFOBT), is a simple stool test used to detect tiny amounts of blood in the bowel motion that are not visible to the naked eye.

The presence of blood may be an early sign of bowel cancer, bowel polyps, or other conditions affecting the colon. FOBT is commonly used as a screening test in people without symptoms.

2. Why Is FOBT Important?

FOBT plays a key role in bowel cancer screening. It helps identify people who may have early bowel cancer or pre-cancerous polyps before symptoms develop.

In Australia, FOBT is offered as part of the National Bowel Cancer Screening Program to eligible age groups. Early detection through screening significantly improves outcomes and reduces deaths from bowel cancer.

Data from the Australian National Bowel Cancer Screening Program show that approximately 6–8% of people who complete an iFOBT will have a positive result and be referred for further investigation.

Among people who proceed to colonoscopy after a positive iFOBT, around 40–50% are found to have bowel polyps, many of which are pre-cancerous and can be removed during the procedure.

Bowel cancer is detected in approximately 0.5–1% of all people who complete an iFOBT, with cancers often identified at an earlier and more treatable stage through screening.

3. Symptoms & How It May Be Used

FOBT is primarily a screening test and is used in people who do not have bowel symptoms.

In some cases, FOBT may also be used to investigate unexplained iron deficiency anaemia or subtle bowel symptoms. It is important to note that a normal FOBT does not exclude bowel cancer in someone with symptoms.

4. How Is FOBT Performed?

FOBT involves collecting small samples from bowel motions at home using a test kit. The samples are then returned for laboratory analysis.

No dietary restrictions are usually required for iFOBT. The test is simple, non-invasive, and can be completed in privacy at home.

5. What Do the Results Mean?

A negative FOBT means no blood was detected at the time of testing, but it does not guarantee that bowel cancer is not present.

A positive FOBT means blood was detected. This does not automatically mean cancer, but it does indicate the need for further investigation, usually with a colonoscopy, to identify the source of bleeding.

6. Living With / Managing a Positive FOBT

If your FOBT is positive, timely follow-up is important. Most people with a positive FOBT do not have cancer, but further testing is essential to rule out serious causes.

Colonoscopy allows direct examination of the bowel and removal of polyps if present. Early investigation leads to better outcomes.

7. Prevention & Risk Reduction

Regular participation in bowel cancer screening programs is one of the most effective ways to reduce the risk of dying from bowel cancer.

Maintaining a healthy lifestyle, including a balanced diet, regular exercise, limiting alcohol intake, and avoiding smoking, also reduces bowel cancer risk.

8. When to Seek Medical Advice

You should seek medical advice if you have a positive FOBT, bowel symptoms such as bleeding, persistent change in bowel habits, unexplained weight loss, or iron deficiency.

FOBT should not be used to delay investigation in people with symptoms or those at higher risk of bowel cancer.