Universal human immunodeficiency virus (HIV) screening was recommended in 2012, 
and major improvements in HIV testing have occurred in the past decade, but 
identification of HIV infected individuals remains inadequate in the United 
States. We report the case of a seronegative HIV-infected man who despite 
clinical and laboratory findings of acquired immunodeficiency 
syndrome,repeatedly tested nonreactive to third-generation HIV enzyme 
immunoassays (EIAs) and Western blot testing. Serologic diagnosis in this case 
required fourth-generation EIA testing due to the seronegativity of standard 
testing. The fourth-generation HIV EIA was positive presumably because it 
detects p24 HIV antigen as well as antibodies, unlike rapid HIV tests and 
third-generation HIV EIAs.This case highlights not only the importance of 
frontline providers to understand the different testing methodologies for HIV 
screening and their limitations but the importance of clinical suspicion as 
well.