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

BACKGROUND: In 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. METHODS: We 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. RESULTS: During 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%). CONCLUSION: We 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. [Image: see text] DISCLOSURES: All authors: No reported disclosures.