Data Suggests New Antigen-Antibody Combo Test Useful for High Volume Public Health Screening

Montreal — A new HIV antigen-antibody combination assay, currently available in Europe, can be useful for high-volume screening to identify individuals with acute HIV infection, who would be missed by traditional HIV antibody tests, according to research presented by Johns Hopkins University, Abbott and others at the 16th Conference on Retroviruses and Opportunistic Infections (CROI).

“Those with recent HIV infections who have not yet developed an HIV antibody response are a major driver of the global HIV epidemic,” said John Hackett, Ph.D., from the Global HIV Surveillance Program at Abbott. “The current method for detection of acute infections is expensive and labor-intensive pooled nucleic acid testing (NAAT). The combination assay represents a reliable and cost-effective alternative with important benefits for HIV prevention strategies.”

Acute HIV infection, the early phase of infection when symptoms begin to emerge, cannot be detected by most routinely used serological HIV tests. Conventional HIV tests detect HIV-specific antibodies in blood or oral fluids that are produced by the immune system during seroconversion or the development of detectable antibodies, which occurs approximately 22 to 25 days after initial infection. Therefore, a person infected very recently may receive an HIV-negative result using conventional HIV tests.

Testing for the antigen reduces the “window period” in which an individual may have been exposed to HIV and have a reactive test result. This means that individuals exposed to HIV may test reactive for the antigen, but may not test reactive to the antibody.
Johns Hopkins and Abbott Study Results

In the study by Johns Hopkins and Abbott, blood samples were collected every six months from men who have sex with men (MSM) participating in the U.S.

Behavioral Intervention Study (EXPLORE). The men were HIV antibody negative at enrollment in the study. The previous seronegative specimens from patients who subsequently tested HIV antibody positive were tested individually with two different HIV RNA assays. Those determined positive by both methods were

classified as acute infections. The specimens were then tested with the Abbott ARCHITECT® HIV Ag/Ab (antigen/antibody) Combo assay and two third-generation HIV antibody tests.

The Abbott combination assay detected 61.9 percent (13) of the acute infections. Only 14.3 percent (3) of the acute samples were identified as positive by one of the third-generation antibody tests. There were a total of 21 acute infections among 217 samples from seronegative individuals.

“The HIV Combo assay detected nearly two-thirds of early, acute HIV infections in a high-risk population, suggesting that this test can be useful for high-volume public health outreach screening to identify acute HIV infections,” Hackett said.
University of Washington, Kings County and Seattle Public Health

In another study presented at CROI, researchers from the University of Washington, Kings County and Seattle Public Health tested 14,005 MSM with HIV antibody tests from 2003 through 2008. Overall, 328 individuals (2.3 percent) were positive for HIV antibodies, and 36 of those who tested negative were classified as positive after pooled HIV RNA testing. The HIV antibody tests detected 90 percent of the infected samples.

Sixteen of the 36 samples that tested negative for HIV antibodies and positive with the RNA test were then tested with the Abbott HIV Ag/Ab Combo assay. Of the 16 RNA-positive samples, 15 (94 percent) were detected by the Abbott HIV/Ab Combo assay. “This study indicates that the HIV antigen-antibody combination assay could be an effective alternative to NAAT for identifying acute HIV infections,” Hackett said.

The Abbott ARCHITECT® HIV Ag/Ab Combo assay is currently in development and not available in the United States.