American Board of Internal Medicine (ABIM) Certification Practice Exam

What test is used to rule out the antibody-negative "window period" of acute HIV infection?

1. CD4 count testing

2. HIV NAAT to detect viral RNA

3. Western blot testing

4. Rapid test

The correct answer is: HIV NAAT to detect viral RNA

The test used to rule out the antibody-negative "window period" of acute HIV infection is the HIV NAAT (Nucleic Acid Amplification Test) to detect viral RNA. During this window period, an individual infected with HIV may not yet produce antibodies that can be detected by standard antibody tests, such as rapid tests or Western blot tests. However, the virus is typically present in the blood and can be detected through nucleic acid testing that measures the amount of viral RNA. HIV NAAT is particularly significant in early detection of the infection because it can identify the virus itself, allowing for timely diagnosis and treatment. This testing method is more sensitive compared to tests that rely solely on the presence of antibodies and is essential in situations where acute HIV infection is suspected despite negative antibody tests. In contrast, other tests like CD4 count testing are not useful for diagnosing acute HIV, as they measure the immune system's response rather than the presence of the virus itself. Rapid tests and Western blot testing depend on the presence of antibodies and therefore are not effective during the early window period when no antibodies may be present yet.