Report in English with a Dutch summary (KCE reports 45A)

64 Screening for Colorectal Cancer KCE reports vol.45
Aside from the classical guaiac FOBT there has been the development of
immunochemical FOBTs (iFOBT) specifically designed to detect human
hemoglobin in dried fecal samples. They contain polyclonal anti-human
hemoglobin antibodies that react with the globin portion of undegraded
hemoglobin. Because they are specific for human blood in feces, no special
dietary restrictions are required 270. Restrictions on intake of drugs that easily
induce gastro-intestinal erosions and hemorrhage, however, remain.
Hemoglobin from upper G.I. bleeding (i.e., oral cavity, oesophagus, stomach or
small intestine) is generally degraded by bacterial and digestive enzymes before
reaching the large intestine and is therefore rendered immunochemically nonreactive.
Conversely, hemoglobin from lower G.I. bleeding (i.e., caecum, colon
or rectum) undergoes less degradation and can therefore remain
immunochemically reactive. Thus, immunochemical fecal occult blood tests
which detect undegraded hemoglobin have, in theory, increased biological
specificity for lower G.I. bleeding and any associated pathology 270, and therefore
could lower the overall cost of detecting these disorders by lowering
colonoscopy rates 196, 202-205. However, we have to keep in mind that all fecal
occult blood tests are subject to certain limitations inherent to lesions that
bleed intermittently with non-uniform distribution of blood in feces. There is
much variation between iFOBT tests and they are more expensive. They are
also less studied than the classic gFOBT test.
Immunochemical FOBTs require sample collection from 2 stools (InSure OC-
Hemodia), 3 stools (HemeSelect, FlexSure OBT, MonoHaem), or 1 stool
(Instant-View, immoCARE) 270. For InSure the sample is collected by brushing
the surface of the stool while in the toilet bowl water, avoiding the gFOBT
requirement for dry specimen collection, which is easier to handle and thus
claimed to be more patient friendly and thereby increase screening
compliance 201.
The test formats for several iFOBTs require minimal processing and involve
developing a test strip with controls and reading a colour reaction. Some iFOBT
formats require more extensive laboratory processing (HemeSelect, OC-
Hemodia). In the case of the InSure, all tests are exclusively developed by a
private laboratory company (U.S.). Magstream 1000 271, 196, 202 and Hem SP
272, 273
provide automatic instrumental test development and reading with adjustable
sensitivity threshold.
Advantages and disadvantages of iFOBT compared with gFOBT are summarized
in Table 14.