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Colonoscopy is generally recommended as the preferred follow-up test to a positive FOBT.
Factors that can cause this test to be less accurate include the following:
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Bleeding gums following a dental procedure
- Ingestion of red meat within 3 days
- Ingestion of fish, turnips, or horseradish
Drugs that can cause GI bleeding include anticoagulants, aspirin, colchicine, iron supplements in large doses, NSAIDs (anti-inflammatory analgesics), and corticosteroids.
Drugs that can cause false positive measurements include colchicine, iron, oxidizing drugs (for example, iodine, bromides, and boric acid), and reserpine.
Large amounts of vitamin C can cause false-negative results on most FOBTs.
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