Guaiac testing of stool for occult blood is a commonly used screening test for colorectal cancer. Patient preparation is necessary to reduce the frequency of false-positive results.
(1) While a single test may be done without patient preparation, patient preparation is indicated before conducting a screening test series (usually 3 tests).
(2) If persistent positive results are found on a test series, then colonoscopy is usually performed.
Medicines to avoid for 72 hours prior to and during testing because of potential gastrointestinal irritation and/or increased bleeding:
(1) aspirin (low dose for cardiovascular disease prophylaxis can be continued)
(2) other NSAIDS
(3) oral iron, only if irritating
Medicines or vitamins causing false negative results:
(1) ascorbic acid (reducing agent): discontinue 5 days prior to testing
Foodstuffs to avoid because of peroxidase-like substances for 3-5 days before and during the test period (false positives):
(7) bean sprouts
Conditions requiring a delay in testing:
(3) dental work with bleeding
(4) known upper GI bleeding
Foodstuffs containing blood should be stopped for 72 hours prior to testing and through test period:
(1) red meat
(2) black (blood) pudding
Suggested meat-free diet starting the day before and during test period:
(1) vegetables, raw and/or cooked: lettuce, spinach, corn
(2) fruits not listed above
(4) roughage with popcorn and peanuts
Sources of false positive for specimens collected from within the toilet:
(1) toilet bowl sanitizers
(2) blood in toilet from other sources
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