A faecal immunochemical test (FIT) is a test for human haemoglobin in stool as a screening tool for colorectal carcinoma. It is considered a better test than the traditional guaiac faecal occult blood test (gFOBT) which cannot distinguish human blood from food-derived sources.
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Technical background
A faecal immunochemical test uses an antibody-based assay for the globin component of the haemoglobin molecule 2. The laboratory assay employs an automated immunoturbidometric test. Point of care assays use a form of immunochromatography 2.
There are a very large number of faecal immunochemical tests on the market and they are not equivalent in their accuracy 2.
Accuracy
Clearly, depending on the level of faecal haemoglobin used as a cut-off value, the sensitivity and specificity of the faecal immunochemical test will vary.
History and etymology
The guaiac-based test has been in regular clinical use for a very long time, first being developed in the 1860s. Faecal immunochemical tests were introduced in the 1970s 2.
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