The faecal occult blood test (FOBT) is a test that can detect tiny traces of blood in the stool — such small traces that they can’t be seen with the naked eye. Occult literally means hidden or unknown. The test can indicate the presence of disease at a relatively early stage when stools may appear normal.
Two types of faecal occult blood test are commonly used — a chemical test (based on a chemical reaction to haem — part of haemoglobin, the oxygen-carrying molecule found in red blood cells) and an immunological test (using antibodies that recognise haemoglobin).
Blood in your stool indicates there is bleeding somewhere in your digestive tract. Any bleeding from the bowel or blood in the stool should be followed up with your doctor.
Sometimes this type of bleeding can be caused by conditions such as haemorrhoids, but it can be a symptom of serious diseases, such as bowel (colorectal) cancer, which is why it is important to make an appointment to discuss it with your doctor.
The test is used as a screening test for bowel cancer or to find out if there is bleeding from the digestive system if you have abdominal symptoms.
The test isn’t usually given to people who can already see blood in their stool or who have symptoms such as anaemia, persistent change in bowel habits, unexplained weight loss or bleeding from the rectum. In these cases, more in-depth investigations will be done.
The Cancer Council Australia and the National Health and Medical Research Council recommend starting 2-yearly faecal occult blood testing from the age of 50 in people who do not have any symptoms or a strong family history of bowel cancer.
The Cancer Council advises that people who are at high risk of bowel cancer — those with close relatives who have had the disease or those who have a condition that increases the risk of bowel cancer — should discuss screening options with their GP.
The Government has phased in a National Bowel Cancer Screening Program using faecal occult blood tests. Screening is currently offered to people turning 50, 55 or 65 years of age between 1 January 2008 and 31 December 2010, and who hold a Medicare card or a DVA gold card. If you are eligible, you will be sent an invitation to complete a faecal occult blood test free of charge. You can complete the test at home and post it to a lab for analysis.
If you are not eligible for the screening programme, you can obtain a faecal occult blood test from your doctor or buy one from a chemist.
For some types of faecal occult blood test, you may need to avoid certain foods and medicines for a few days before doing the test and throughout the testing period. If the test instructions advise such dietary restrictions, ensure that you follow them to avoid a misleading result.
You should avoid doing a faecal occult blood test during or within 3 days of a menstrual period, if you have haemorrhoids (piles) that are bleeding or if blood is visible in your urine or in the toilet bowl — in which case you should see your doctor.
With some bowel diseases, blood may not be present in the stool every day, so you may be advised to test your stools on several different days.
Some tests involve smearing a small sample of stool onto a test card that is chemically treated. There are also newer types of FOBT, which involve testing the toilet water above the surface of the stool in the toilet bowl. With others you can use a scraper to take a stool sample off toilet paper that you have just used. Another chemical is then added to the test card. If there is blood in the stool, the test card will change colour. Instructions should be included with the test.
If your test result is positive, you will be asked to contact your doctor. A positive test does not necessarily mean that you have cancer, but you will need further examinations, such as colonoscopy or biopsy, to determine the cause of the bleeding. Your doctor will be able to arrange these examinations.
You should also bear in mind that a negative result is not an absolute guarantee that you don’t have bowel cancer. So you should have another faecal occult blood test every 2 years and see your doctor promptly if you develop any of the symptoms described above.
If bowel cancer is detected early, or in its pre-malignant (pre-cancerous) stage, there is a good chance of prevention or cure.
Last Reviewed: 12 February 2010