American Board of Internal Medicine (ABIM) Certification Practice Exam

In patients with chronic H. pylori infection, which of the following can lead to false-negative results in testing?

1. Fecal antigen test

2. Serologic antibody testing

3. Urea breath test

4. All of the above

The correct answer is: All of the above

In the context of chronic H. pylori infection, false-negative results can occur with various diagnostic tests due to several factors, including the specific characteristics of the tests themselves and the patient's clinical situation. Fecal antigen tests can yield false negatives, particularly if the patient has recently undergone therapy such as antibiotics or proton pump inhibitors, which can suppress H. pylori antigens in the stool. Similarly, serologic antibody testing is influenced by the patient's immune response; in some cases, antibodies may not be produced in detectable levels due to chronicity or a waning immune response, especially if the infection is longstanding. The urea breath test, while generally reliable, can also produce false-negative results under certain conditions, such as use of antibiotics, antisecretory medications, or if the patient has a low bacterial load that doesn’t generate enough carbon dioxide for detection. Therefore, all these testing methods have vulnerabilities that can lead to inaccurate results, particularly in the presence of a chronic infection where bacterial load and immune responses may vary. Understanding these limitations is crucial for accurate diagnosis and management of H. pylori infections.