Interpretation of HIV Serologic Testing Results

Abstract

A 33-year-old male patient visited the outpatient clinic at Brigham and Women's Hospital for a routine follow-up for obesity, obstructive sleep apnea, allergic rhinitis, and depression. He was maintained on a nocturnal continuous positive airway pressure device, loratadine, duloxetine, and fluticasone nasal spray. He was a resident of Boston and had not traveled outside the country. He denied intravenous drug use or high-risk sexual behavior, and he had not received any blood products. He had received his most recent influenza vaccine about 6 months earlier. He was screened for type 2 diabetes and hyperlipidemia. As a part of routine clinical care, he was also offered HIV screening in accordance with the current CDC recommendations (1). The HIV assay [HIV 1/O/2 Enhanced (EHIV)], which was performed on the ADVIA Centaur analyzer (Siemens Healthcare Diagnostics), yielded a reactive result. As per the assay protocol developed by the manufacturer, the initially reactive sample was retested in duplicate after centrifugation; both results were reactive. The positive screen was followed up with a confirmatory western blot (WB)3 analysis, which yielded an indeterminate result. The presence of an isolated p24 band in the WB (GS Western HIV-1; Bio-Rad Laboratories) was of concern regarding possible early HIV seroconversion. ### QUESTIONS TO CONSIDER 1. What factors are known to cause false-positive HIV serologic test results? 2. What factors are known to cause an indeterminate WB result? 3. What further testing or clinical history would be of help in evaluating a patient with an indeterminate WB result? The Siemens EHIV screen performed in this case is a double antigen-bridging microparticle chemiluminometric immunoassay that detects antibodies against p24, gp41, gp120 (from HIV-1), gp36 (from HIV-2), and a synthetic peptide from group O HIV-1 (Fig. 1). A positive result indicates the presence of antibodies that recognize any of these antigens, regardless of their isotype or subclass. Although …