American Board of Internal Medicine (ABIM) Certification Practice Exam

What is the role of serologic assays in diagnosing typhoid fever?

1. To detect specific S. enterica serotype Typhi antibodies

2. To assess liver function

3. To determine blood type

4. To evaluate immune response to vaccines

The correct answer is: To detect specific S. enterica serotype Typhi antibodies

The role of serologic assays in diagnosing typhoid fever is primarily to detect specific antibodies against Salmonella enterica serotype Typhi, the bacteria responsible for the disease. In cases of typhoid fever, the immune system produces antibodies in response to the infection, which can be detected through serologic testing. These assays are useful because they provide a means to confirm the diagnosis of typhoid fever, especially when clinical symptoms are present, and cultures may not be available or are not yet positive. The detection of IgM and IgG antibodies specific to S. enterica serotype Typhi indicates active infection or past exposure, helping to differentiate typhoid fever from other febrile illnesses. Other choices do not directly relate to the diagnosis of typhoid fever. Assessing liver function is important for evaluating overall health but is not specific to typhoid fever. Determining blood type is unrelated to the diagnosis of infections. Evaluating immune response to vaccines may be relevant for assessing immunization status but does not specifically address the acute infection in cases of diagnosed typhoid fever. Therefore, serologic assays play a critical role in the diagnosis by confirming the presence of the antibodies specific to the causative agent of typhoid fever.