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. 2013 Jun 21;62(24):489–494.

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Fourth-generation HIV-1/2 immunoassay test results with the new HIV diagnostic testing algorithm — New York, New York; San Francisco, California; and North Carolina, September 2011–2012

**Abbreviations:** HIV = human immunodeficiency virus; NAT = nucleic acid test; IFA = immunofluorescence assay.

* Five of the seven Western blot positive results and two of the four IFA positive results occurred with specimens that were HIV-1 indeterminate on the differentiation assay. The differentiation assay has four reaction spots, including 1) control, 2) HIV-2 peptide, 3) recombinant HIV-1, and 4) HIV-1 peptide. When used in a diagnostic algorithm, both HIV-1 spots (recombinant and peptide) must be reactive for a specimen to be interpreted as positive for HIV-1 antibodies. The presence of only one HIV-1 spot is interpreted as indeterminate for HIV-1 antibodies.

FIGURE 2.