Variability in HIV seropositivity by confirmatory assays should be considered for both initial diagnosis and multicenter studies for which inclusion criteria require serologic profile confirmation, according to a study recently published in Open Forum Infectious Diseases.

Treatment is recommended for any individual who is newly diagnosed with HIV-1 infection, regardless of the stage of infection. However, for clinical decision-marking and prevention, it is useful for persons to be identified within weeks of HIV-1 antibody conversion.  Acute HIV-1 infection, which is defined biologically as the period from HIV blood detection until seroconversion, is usually easily diagnosed based on the presence of the p24 antigen. Therefore, interpreting HIV test results during this brief window can provide an accurate estimation of time of infection. However, after HIV antibody seroconversion the identification of a recent HIV infection at diagnosis can be challenging but can be suspected when confirmed with a Western blot or immunoblot assay. To this end, a study was conducted to evaluate 5 commercially available assays that are approved for HIV seropositivity confirmation and could be readily performed in clinical laboratories.

In total, 5 assays approved for the confirmation of HIV seropositivity by the US Food and Drug Administration and/or European Commission were evaluated, including 2 Western blots (New LAV Blot I, Biorad, France and HIV Blot 2.2, MP Biomedicals, Singapore); 2 immunoblots (INNOLIA HIV I/II, Fujirebio, Ghent, Belgium and RecomLine HIV-1 & HIV-2, Mikrogen Diagnostik, Neuried, Germany); and 1 immunochromatographic single-use assay (Geenius HIV 1/2 supplemental assay, Biorad, Marnes-la-Coquette, France). Serum samples from 43 individuals recently infected with HIV-1 were selected in 2 clinical laboratories in France based on incomplete or weakly reactive Western blots and either a previous sample collected during acute infection (p24 positive) or an evolving Western blot profile on a subsequent serum sample. Results were interpreted either by strictly following the manufacturer’s recommendation or by Fiebig classification: stage I/II/III (no band), stage IV (only 1 band among p24, gp41, and gp120/160), stage V (at least 2 bands among p24, gp41, and gp 120/160 [ie, FDA criteria for HIV seropositivity but without p31], and stage VI (full reactivity including a p31 band).

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The investigators found that there is variability and inconsistency among assays results. When the manufacturer’s recommendations were followed for interpretation, the 2 Western blots showed indeterminate results for 30% (Biorad) and 42% (MP Biomedicals) of the samples, suggesting recent infection. However, the other 3 assays showed similar results for only 2% to 7% of samples. When the Fiebeig classification was followed for interpretation, concordant states were observed in 42% of samples, and only 49% were classified as early seroconversion by all 5 assays. When the remaining specimens were tested, the distinction with chronic infection was highly variable, ranging from 5% to 100%, depending on which assay was used.

Overall, the study authors conclude that, “Our study highlights the difficulties of providing consistent results for identification of recently infected individuals when antibodies are already detectable, particularly when different confirmatory assays and/or different clinical laboratories are involved.”


Stefic K, Mahjoub N, Desouche C, et al. Difficulties of identifying the early HIV antibody seroconversion period depending on the confirmatory assay [published online April 21, 2020]. Open Forum Infect Dis. doi:10.1093/ofid/ofaa140