Faecal Occult Blood Test and Faecal Immunochemical Test

To screen for bleeding from the gut/intestine, which may be an indicator of bowel cancer

The test is used to screen for bowel cancer especially as part of the National Bowel Cancer Screening Programme. It may also sometimes be used when a patient has a family history of cancer of the intestine and some other organs, when symptoms are suspicious of gut cancer or to help diagnose long-term unexplained anaemia if imaging tests, such as colonoscopy, are unavailable.

One or more samples of faeces (stool)

For the guiac-based FOBT (gFOBT), you may be instructed to avoid certain medications and follow certain dietary restrictions for several days before collecting the stool samples. For immunochemical FOBT (iFOBT, FIT), there are no dietary or drug restrictions.

The faecal occult blood test (FOB) or faecal immunological test (FIT) checks for blood in your faeces. Normally, there will not be enough blood lost through the gastrointestinal tract (stomach and intestines) to turn a FOB positive or for you to notice it by looking. Any significant amount of blood being passed (seen as bloody or dark, tarry faeces) should be investigated.

A positive FOB will tell your doctor that you have bleeding occurring somewhere in your gastrointestinal tract. This blood loss could be due to ulcers, diverticulitis, bleeding polyps, inflammatory bowel disease, haemorrhoids (piles), from swallowed blood due to bleeding gums or nosebleeds, or it could be due to benign or malignant tumours. Anything that sticks out into the intestine, like a polyp or tumour, and is rubbed against by the faeces as it passes through, has the potential to bleed now and again. Often this small amount of blood is the first, and sometimes the only, symptom of early bowel cancer, making the FOB a valuable screening tool.

First, your doctor may give you some instructions about dietary restrictions that you should follow and drug treatment that you should avoid before collecting the FOB samples. For example, you should not eat red meat within three days before testing. Other substances that could cause a false positive test result include fish, turnips, horseradish, and drugs such as colchicines and oxidizing drugs (for example, iodine and boric acid). Be sure to carefully follow your doctor's instructions.

You collect tiny faeces samples yourself, in the privacy of your own bathroom, using a special kit.

The main method for faecal occult blood testing is the guaiac smear method (gFOBT), explained below.

Your doctor or laboratory will typically give you three 'cards' so that you can collect samples from three different stools, usually on different days (or one card with three flaps). It is important that the stool sample is not contaminated with urine or water. Suggestions to catch your sample include any clean disposable container or your hand in a small plastic bag. Label the card/flap with your full name and the date; then, with an applicator stick, apply a thin smear of stool onto each filter paper square/window contained on the card, and allow it to dry. Usually you will collect all three samples, then return all of them to your doctor/laboratory at the same time, sometimes by posting them.

An alternative method for faecal occult blood testing is the faecal immunochemical test. The collection method varies between manufacturers. Some use a card similar to that described above. Others use a plastic wand to transfer a small amount of faeces to a tube of liquid. Read all the instructions very carefully before starting to collect your sample.

For guaiac-based FOBT (gFOBT) special dental, dietary and drug restrictions may be recommended. These tests detect any blood that enters the digestive tract. Therefore, steps that are taken to avoid introducing blood into the digestive tract will increase the quality of the test sample.

Check with the doctor before stopping any drugs to be certain that it is safe to do so.

For immunochemical methods (iFOBT, FIT), there are no dietary, drug, or dental procedure restrictions. The test uses antibodies to detect only human blood from the lower digestive tract (colon).

For all tests, follow the instructions that are provided by the doctor or included in test kit. Avoid collecting samples during a menstrual period.

Conditions: Bowel cancer
Screening: Screening Tests for Adults (50 and up)
In the News: Five-minute screen at sixty can cut bowel cancer deaths

NHS Choices
Cancer Research UK
Bowel and Cancer Research
GP Notebook