Which statement about stool antigen test for H. pylori is true?

• A. High sensitivity
• B. Detects antibodies in stool
• C. Requires colon biopsy
• D. Low sensitivity and high false negatives

Answer: (D)

Stool antigen testing for Helicobacter pylori is a noninvasive assay that looks for bacterial antigens in stool to diagnose infection and to confirm eradication after treatment. It does not detect antibodies in stool, so that option is incorrect. It also does not require a colon biopsy, since it’s performed on a stool sample. While modern monoclonal stool antigen tests are generally reliable, their performance can be reduced under certain conditions—such as recent use of antibiotics, proton-pump inhibitors, or other factors that lower bacterial load or affect antigen shedding—leading to false negatives. In those contexts, the test can exhibit lower sensitivity and more false negatives, which is why the statement about low sensitivity and high false negatives is considered true.