Which supplement can cause a false-positive fecal occult blood test?

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Multiple Choice

Which supplement can cause a false-positive fecal occult blood test?

Explanation:
The test detects hidden blood by a peroxidase reaction: heme in blood catalyzes a reaction that turns a guaiac-impregnated paper blue. High-dose ascorbic acid is a strong reducing agent that can quench this color change, leading to a false-negative result. It doesn’t typically cause a false-positive result. If the test used is immunochemical, supplements generally don’t affect it. So the important point is that vitamin C can mask blood in the stool by preventing the color change, not produce a false positive.

The test detects hidden blood by a peroxidase reaction: heme in blood catalyzes a reaction that turns a guaiac-impregnated paper blue. High-dose ascorbic acid is a strong reducing agent that can quench this color change, leading to a false-negative result. It doesn’t typically cause a false-positive result. If the test used is immunochemical, supplements generally don’t affect it. So the important point is that vitamin C can mask blood in the stool by preventing the color change, not produce a false positive.

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