Resolution of a False-Positive Fourth-Generation HIV Screening Test by Polyethylene Glycol Precipitation: A Case Report.

Fourth generation human immunodeficiency virus (HIV) antigen/antibody (Ag/Ab) combination assays are highly sensitive and enable early detection of HIV infection; however, rare false positive results due to immunoassay interference may occur. We report a case of discordant HIV testing characterized by a reactive ARCHITECT HIV Ag/Ab Combo screening assay with negative HIV 1/HIV 2 antibody differentiation and negative HIV 1/HIV 2 qualitative nucleic acid testing. To investigate the mechanism of reactivity, polyethylene glycol (PEG6000) precipitation was performed. Following PEG treatment, the patient's specimen converted to non reactive on repeat screening; comparatively, a confirmed HIV positive control specimen remained strongly reactive, despite partial signal reduction. These findings support the presence of PEG-precipitable immune interference as a likely contributor to false reactivity and highlight PEG precipitation as a useful problem solving tool in selected cases of discordant HIV serologic results.