Abstract
BackgroundHIV screening (i.e. antigen/antibody) tests are followed by a supplemental (i.e. antibody-only) if the screen is positive. Discrepant results can result from two scenarios: a false-positive screening test or acute HIV infection. These scenarios can be distinguished by a molecular HIV test, but due to contamination concerns, our laboratory recently implemented a policy requiring a second specimen dedicated for molecular HIV testing. Our objective was to (1) characterize the effect of this policy on the time-to-diagnosis for patients with discrepant screening and supplemental test results, and (2) explore “strength of positivity” as an interim predictor of screening test accuracy while awaiting confirmatory test results.MethodsData from our laboratory information system, electronic health record, and instrument logs were used to collate data for all HIV testing performed at Barnes-Jewish Hospital (BJH) between January 1, 2014 and October 18, 2017.ResultsRequiring a dedicated specimen for molecular testing significantly increased the time-to-diagnosis for patients with discrepant screening and supplemental HIV tests (p = 0.0084). This policy also contributed to loss-to-followup, with 0/35 discrepant cases lost-to-followup prior to policy implementation compared to 2/10 after implementation. However, by optimizing the signal-to-cutoff (S/CO) ratio of the screening test, we were able to more accurately distinguish false-positives from acute-HIV prior to molecular testing (sensitivity of 100%, specificity of 89%).ConclusionsWe propose utilizing quantitative fourth-generation assay results (S/CO) ratios as a predictor of infection true positivity in situations where the screening assay is reactive but the supplemental test is negative and confirmatory molecular results are not immediately available.
Highlights
The detection of HIV-specific antibodies in a patient’s serum has traditionally been required to make the diagnosis of HIV infection
Discrepant results can result from two scenarios: a false-positive screening test or acute HIV infection. These scenarios can be distinguished by a molecular HIV test, but due to contamination concerns, our laboratory recently implemented a policy requiring a second specimen dedicated for molecular HIV testing
We propose utilizing quantitative fourth-generation assay results (S/CO) ratios as a predictor of infection true positivity in situations where the screening assay is reactive but the supplemental test is negative and confirmatory molecular results are not immediately available
Summary
The detection of HIV-specific antibodies in a patient’s serum has traditionally been required to make the diagnosis of HIV infection. Third generation antibody-based assays are likely to miss cases of acute HIV infection, during which time viral loads are high but HIV-specific antibody titers have not yet risen [1, 2]. To address this shortcoming, the US Department of Health and Human Services recommends screening for HIV infection with an assay capable of detecting both HIV antibodies and HIV p24 antigen–a “fourth-generation” assay–as the first step in a sequential HIV testing algorithm. Our objective was to (1) characterize the effect of this policy on the time-to-diagnosis for patients with discrepant screening and supplemental test results, and (2) explore “strength of positivity” as an interim predictor of screening test accuracy while awaiting confirmatory test results
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