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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 COPYRIGHT © SULLIVAN NICOLAIDES PATHOLOGY 2013 IP605 APRIL 2015