Faecal occult blood testing for population health screening May 2004

Executive summary
The procedure
Faecal occult blood tests (FOBTs) are used to detect blood in faeces that is not obvious
by general inspection (ie, occult blood). This technology has been utilised for both
diagnostic and screening purposes; however, the purpose of this review is to investigate
the relative performance of different FOBTs for population health screening. The review
was undertaken to provide support to the Australian Government Bowel Cancer
Screening Pilot Program (the pilot).
There are two types of FOBTs in common use: the long-established guaiac tests and the
newer immunochemical tests. ‘Two-tiered’ combinations of these tests have also been
developed.
Guaiac FOBTs
The guaiac FOBTs act by detecting the intact haem molecule from haemoglobin. These
tests are simple to perform colorimetric tests, often conducted in the home. Two small
samples from stools obtained on three consecutive days are applied to a piece of paper
impregnated with guaiac gum. Upon application of a developing solution, the presence of
trace amounts of haem results in a blue colour change due to the pseudo-peroxidase
actions of haem. Guaiac FOBTs are able to detect bleeding originating anywhere
between the mouth and anus. However, the sensitivity of guaiac FOBTs for detecting
upper gastrointestinal (GI) bleeding is less than for the lower GI tract. The accuracy of
guaiac FOBTs can be affected by several factors including medications, diet and
excessive amounts of reducing agents in faecal samples (eg, vitamin C).
The guaiac FOBTs include brand names such as: Hemoccult, Hemoccult II, Hemoccult
Sensa, Hemo FEC, Coloscreen, Fecatest (discontinued) and Shionogi B. The two
versions of the Hemoccult test (Hemoccult and Hemoccult II) differ only with regard to
their configuration, therefore this document will refer to both versions simply as
Hemoccult, without differentiation.
Immunochemical FOBTs
The immunochemical FOBTs involve the use of an anti-human monoclonal antibody,
targeted at intact human blood-borne proteins (usually haemoglobin). These tests
therefore have the theoretical advantage of not being affected by haem, peroxidases or
anti-oxidases in the diet. In addition, immunochemical tests will not detect proximal
bleeds, since in this case haemoglobin will be digested before being passed in the faeces.
However, these tests are generally more complex and expensive than the guaiac tests and
often require laboratory processing.
The immunochemical FOBTs include brand names such as: HemeSelect (discontinued)
and Immudia-HemSp (international equivalents), FlexSure OBT (discontinued),
Quicktest, DIMA FOB-10, Bayer Detect, Magstream HemSp, !nSure, !nForm and
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