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BioRad BioPlex® HIV Ag-Ab assay: Incidence of false positivity in a low-prevalence population and its effects on the
Jayme Parker1, Ana Fiorella Carrasco2, Jack Chen1
1Department of Health and Social Services, Division of Public Health, Alaska State Public Health Virology Laboratory, Fairbanks, Alaska, United States; Department of Biology and Wildlife, Institute of Arctic Biology, University of Alaska -Fairbanks, Fairbanks, Alaska, United States.
Background:
The BioPlex® HIV Ag-Ab assay, unlike other HIV 1/2 antigen/antibody immunoassays, is capable of differentiating positive HIV-1 antibodies (Groups M and O) from HIV-2 antibodies and/or HIV-1 p24 antigen in a single test.
Objective:
The Alaska State Virology Laboratory (ASVL) adopted the BioPlex® HIV Ag-Ab assay early 2017 and can report on its performance in terms of false positivity in a low-prevalence population and its effects on the current HIV testing algorithm recommended by the Centers for Disease Control and Prevention (CDC).
Study Design:
Specimens received between March 2017 and August 2018 were screened using the BioPlex® HIV Ag-Ab assay. Specimens screening positive for HIV antibodies or antigen were further confirmed using the Geenius™ HIV 1/2 Supplemental Assay and/or HIV RNA testing.
Results:
Of the 12,338 sera screened by the BioPlex assay for HIV, 35 specimens were positive. Only 22 of the specimens were confirmed by supplemental testing and were considered to be truly positive (PPV, 62.9%). RNA was not detected in these cases suggesting initial false positivity on the BioPlex® HIV Ag-Ab assay. True positive results had index values (IDX) of >180 whereas false positive IDX's were between 1 and 4, with the exception of one specimen.
Conclusions:
We suggest that specimens demonstrating positivity with low IDX values <4 on the BioPlex® HIV Ag-Ab assay proceed directly to RNA testing, essentially bypassing supplemental antibody confirmation tests, to reduce turnaround time and cost of HIV confirmation.
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