1299. Cluster of False-Positive “Fifth-Generation” HIV Test Results During Implementation of a Routine HIV Screening Program in an Emergency Department

Abstract

BackgroundIn November 2014, the University of Illinois Hospital (UI Health) introduced an electronic medical record (EMR)-driven HIV screening program in the emergency department (ED). In October 2016, our hospital laboratory introduced “Fifth-generation” HIV testing using the Bio-Rad BioPlex 2200 HIV Antigen/Antibody diagnostic assay. Fifth-generation HIV testing has the advantage of separately detecting and reporting HIV antibody and HIV-1 p24 antigen. Although the literature and manufacturer report high sensitivity and specificity of this test, we encountered higher than expected rates of false-positive tests during the introduction of this test.MethodsWe retrospectively reviewed the results of our ED HIV screening program from October 2016 to March 2019 to describe the outcomes of HIV testing, determine the rates of false-positive HIV tests and determine if false-positive rates were temporally clustered. We also investigated various potential causes of higher than expected false positives including pre-analytical and analytical error. We defined a false-positive test as a repeatedly reactive initial HIV antigen and/or HIV-1 antibody result with a subsequent negative or indeterminate HIV-1/2 antibody differentiation immunoassay and negative HIV-1 nucleic amplification test.ResultsDuring the review period, out of a total of 17,385 HIV tests which were performed, 85 tests were confirmed positive and 27 were false positives. This represents an HIV prevalence of 0.5%. Eighteen of the 27 false positives occurred during an 8 month period between October 2016 and April 2017 (see Figure 1). During our investigation of potential causes of the false-positive tests, we discovered that a reagent lot for the test was changed in June 2017 which resulted in a significant decrease in the false-positive rate (0.33% to 0.07%).ConclusionWe provide data which suggests that a reagent lot may have been the cause of higher than expected false-positive tests for HIV testing. Monitoring of testing outcomes during implementation of a routine HIV testing program can help identify potential root causes of false-positive tests. Disclosures All authors: No reported disclosures.