Which statement about guaiac stool testing is supported by the information?

• A. Vitamin C intake can cause a false-negative result
• B. Vitamin C intake can cause a false-positive result
• C. Red meat has no effect on the test
• D. Diet does not affect the test

Answer: (A)

Guaiac stool testing relies on a color change driven by a peroxidase-like reaction from hemoglobin. When daily foods or supplements are involved, substances that interfere with this reaction can alter the result.

Vitamin C is a strong reducing agent. It can neutralize the oxidative process needed to produce the blue color in the guaiac test. Because of this, even if occult blood is present, the test may not develop the blue color—giving a false-negative result. That’s why vitamin C intake can lead to a false-negative outcome.

Dietary factors do affect the test, so statements denying any dietary impact aren’t accurate. For example, red meat contains heme with peroxidase activity and can influence results if consumed before testing, potentially causing false positives. The test can be affected by diet in multiple ways, so diet does matter.

So, the statement that vitamin C intake can cause a false-negative result is the best choice because it directly reflects how a reducing agent like vitamin C can mask true occult blood presence in the guaiac test.