HIV False-Positive Test in the Setting of CD4 Lymphocytopenia

In 2016, we implemented a non-targeted Emergency Department (ED)-based HIV screening program at our academic medical center following revised CDC guidelines utilizing the Abbott Alinity 4th generation HIV-1/2 antigen (Ag)/antibody (Ab) immunoassay (Abbott Laboratories, Abbott Park, IL). Following the CDC algorithm, after reactive fourth-generation testing, HIV-1/2 Ab testing is conducted. Patients undergoing acute seroconversion (acutes) may express p24 Ag but have a negative confirmatory Ab test. Acutes have the same laboratory signature during the ED encounter as those that are false positive (False +), and the two patient groups are denoted as "equivocals" until viral load testing specifies a definitive HIV status. Among False + patients (Ab/Ag positive, Ab negative, viral load undetectable), there have been limited studies on those also demonstrating a reduction in CD4+ count, an uncommon phenomenon known as "idiopathic CD4 lymphocytopenia." We review a patient with a reactive fourth-generation HIV Ab/p24 Ag test on two separate occasions. Despite lymphopenia with a reduced CD4 count, his symptoms resolved, and an RNA PCR test did not detect any presence of HIV (False +). This patient was unique as False + patient with p24 Ag reactive, as well as a coincidental low CD4 count in the absence of HIV infection. A low CD4 count is often a sign of significant HIV infection.