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.
Testing protocols:
(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
(4) cimetidine
Medicines or vitamins causing false negative results:
(1) ascorbic acid (reducing agent): discontinue 5 days prior to testing
(2) antacids
Foodstuffs to avoid because of peroxidase-like substances for 3-5 days before and during the test period (false positives):
(1) turnips
(2) horseradishes
(3) artichokes
(4) mushrooms
(5) radishes
(6) broccoli
(7) bean sprouts
(8) cauliflower
(9) apples
(10) melons
(11) oranges
(12) bananas
(13) grapes
Conditions requiring a delay in testing:
(1) hemorrhoids
(2) menstruation
(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
(3) bran
(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
Specialty: Gastroenterology
ICD-10: ,