Exam Guide
Fecal Occult Blood Test Teaching: Vitamin C
Health Assessment & Documentation · Question from the ATI PN Fundamentals 2023 Proctored Exam study set
Correct answer: "Discontinue supplements containing vitamin C 24 hours before the test."
Why this is the answer
Vitamin C can interfere with the chemical (guaiac) reaction used in some FOBT kits and cause a false-negative result, so it should be avoided before testing.
The bigger concept
Specimen-collection teaching items hinge on what causes false results. For guaiac-based FOBT, vitamin C above 250 mg/day can mask bleeding (false negative), while red meat, raw turnips and horseradish, NSAIDs, and aspirin can cause false positives. Most kits call for a three-day dietary preparation and samples from three separate stools. The PN/VN teaches the preparation and confirms the client understands not to contaminate the sample with urine or toilet water.
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