Download Faecal occult blood testing

Faecal occult blood testing
Faecal occult blood tests are used to screen for colorectal
carcinoma. These tests are not appropriate for the detection
of upper gastrointestinal tract (GIT) bleeding.
Testing methods
Immunochemical testing, which utilises antibodies against
human haemoglobin, is now preferred. Chemical (guaiac acid)
testing, which detects the pseudoperoxidase activity of haem
that forms following the breakdown of haemoglobin, as occurs
in upper GIT bleeding, is no longer performed. Immunochemical
tests (with a lower limit of detection of 50 ng/mL haemoglobin)
are more sensitive than chemical tests.
Patient preparation
A number of drugs can cause bleeding from the gut and
where possible should be avoided in the two days leading
up to the test. These include:
•Excessive alcohol
•Drugs that cause gastrointestinal bleeding
(e.g. aspirin in doses > 325 mg/day)
•Non-steroidal anti-inflammatory drugs (NSAIDs)
(e.g. ibuprofen, indomethacin, and naproxen)
•Corticosteroids
•Phenylbutazone
•Reserpine
•Anticoagulants
•Antimetabolites
•Cancer chemotherapeutic drugs.
No specific dietary restrictions prior to immunochemical testing
are necessary. Red meats, certain raw fruits and vegetables
(melon, carrots, and radish), iron supplements, and excessive
vitamin C supplements do not interfere with the reading of
immunochemical tests as they do with chemical tests.
Specimen collection
Step 1: Order a Faeces Occult Blood sampling bottle through
Supply or instruct patient to pick one up at a Collection Centre.
Step 2: Place a clean receptacle into a toilet bowl and use this
to catch faeces.
Step 3: Using the sampling probe, collect a walnut-sized
sample (10 g) of fresh faeces by direct inoculation into the
sampling bottle. As gastrointestinal bleeding may be intermittent, collect specimens from 3 successive bowel motions.
Greater sensitivity is achieved by sampling the stool surface.
Step 4: Store the specimen bottles at room temperature
after collection, and send specimens to the lab in separate
containers. Testing should be performed within 7 days
of collection.
NHMRC guidelines
Australian Cancer Network Colorectal Cancer Guidelines
Revision Committee. Clinical Practice Guidelines for the
Prevention, Early Detection and Management of Colorectal
Cancer. Sydney: The Cancer Council Australia and Australian
Cancer Network, 2005.
Available online at: http://www.nhmrc.gov.au/publications/
synopses/cp106/ cp106syn.htm
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IP605 APRIL 2015