American Board of Internal Medicine (ABIM) Certification Practice Exam

What testing is utilized to diagnose acute HIV infection?

1. ELISA test for antibodies

2. RNA polymerase chain reaction or p24 antigen testing

3. Western blot testing

4. CD4 count assessment

The correct answer is: RNA polymerase chain reaction or p24 antigen testing

The diagnosis of acute HIV infection relies on testing methodologies that can detect the virus or its components early in the infection process, before the immune system has developed a significant antibody response. This typically occurs within the first few weeks post-exposure. The RNA polymerase chain reaction (PCR) test or p24 antigen test are particularly valuable in this early detection phase. The RNA PCR test directly measures the amount of HIV RNA present in the blood, allowing for the identification of active infection as soon as the virus enters the bloodstream. Likewise, the p24 antigen test detects the p24 protein, a core protein of the HIV virus, which also appears early in infection. In contrast, the ELISA test for antibodies is used primarily to diagnose HIV infection through the detection of antibodies that the body develops in response to the virus. Because antibodies take time to form after exposure, this method is not effective for diagnosing acute HIV infection. Similarly, Western blot testing is used as a confirmatory test after an initial positive result from tests like ELISA, but it is not suited for early detection. CD4 count assessment is primarily used to monitor the immune status of individuals with chronic HIV infection, not for diagnosing newly acquired infections. Thus, for early detection of acute HIV