This case illustrates a scenario that clinicians are likely to encounter more frequently as HIV screening becomes increasingly integrated into routine clinical care. Nonspecific antibody cross-reactivity with the HIV p24 antigen in persons who are not infected is the most common cause for repeatedly reactive HIV-screening assay and indeterminate Western blot results. However, because third-generation (IgM-sensitive) screening assays such as the EHIV (Siemens) detect antibodies 2 or more weeks before bands appear on the Western blot, indeterminate results can also indicate very recent HIV infection. Usually, p24 or gp41 bands are the first to appear on the Western blot after infection. Further complicating this presentation, influenza vaccination has also been implicated as a cause of a reactive HIV screening assay with indeterminate Western blot results. Such cases, however, are usually characterized by Western blot reactivity to the gp160 (precursor) or gp41 (transmembrane) proteins because of the striking homology between the transmembrane molecules of the HIV-1 envelope proteins and the influenza envelope protein hemagglutinin. Despite the absence of classical risk factors for HIV, it remains important to ensure that patients with indeterminate Western blot results are not infected. Recent observations have demonstrated that as many as 50% of persons whose HIV infection is discovered during routine screening do not manifest traditional risk factors. Resolution of an indeterminate Western blot result requires either the qualitative RNA diagnostic assay or quantitative RNA viral load to document absence of HIV RNA or a repeat Western blot after 4 weeks. Negative RNA results or repeatedly indeterminate Western blot results ≥4 weeks apart confirm the absence of HIV infection and allow patients to be reassured that they are uninfected.
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Authors' Disclosures of Potential Conflicts of Interest: No authors declared any potential conflicts of interest.
Role of Sponsor: The funding organizations played no role in the design of study, choice of enrolled patients, review and interpretation of data, or preparation or approval of manuscript.
- Received for publication July 22, 2010.
- Accepted for publication July 26, 2010.
- © 2010 The American Association for Clinical Chemistry