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Epidemiological data indicate that AIDS is caused by at least 2 types of HIV. The first virus, HIV-1, has been isolated from patients with AIDS, AIDS-related complex, and asymptomatic infected individuals at high risk for AIDS. HIV-1 is transmitted by sexual contact, exposure to infected blood or blood products, or from an infected mother to her fetus or infant. A second HIV virus, HIV-2, was isolated from patients in West Africa in 1986. HIV-2 appears to be endemic only in West Africa, but it also has been identified in individuals who have lived in West Africa or had sexual relations with individuals from that geographic region. HIV-2 is similar to HIV-1 in its morphology, overall genomic structure, and its ability to cause AIDS.
Antibodies against HIV-1 and HIV-2 are usually not detected until 6 to 12 weeks following exposure and are almost always detected by 12 months. They may fall into undetectable levels in the terminal stage of AIDS.
See HIV Testing Algorithm (Fourth Generation Screening Assay) Including Follow-up of Reactive HIV Rapid Serologic Test Results in Special Instructions.
Diagnosis of HIV-1 and/or HIV-2 infection in cadaveric or hemolyzed serum specimens from asymptomatic patients with or without risk factors for HIV infection (assay kit is FDA-approved for testing cadaveric or hemolyzed blood specimens)
A reactive HIV-1/-2 antibody screen result obtained by EIA suggests the presence of HIV-1 and/or HIV-2 infection. However, it does not differentiate between HIV-1 and HIV-2 antibody reactivity. Diagnosis of HIV infection must be based on results of supplemental tests, such as HIV antibody confirmation/differentiation test (automatically reflexed on all samples with reactive screen test results at an additional charge).
All presumptive antibody-positive test results should be verified by submitting a second serum specimen for retesting.
A negative HIV-1/-2 antibody EIA screen result usually indicates the absence of HIV-1 or HIV-2 infection. However, for specimens that are reactive by the rapid HIV antibody tests, confirmatory testing is recommended even if the EIA results are negative.
This test is not offered as a screening or confirmatory test for blood donor specimens.
This test is not offered for maternal or newborn HIV screening for specimens originating in New York.
The predictive value of a reactive (or positive) test is highly dependent on the prevalence of HIV infection in the population tested; the lower the prevalence of HIV infection, the lower the positive predictive value of the test.
Negative results should be evaluated cautiously if the patient has clinical symptoms and/or a history of high-risk behavior for HIV infection. The CDC recommends confirmatory testing on serum specimens that are reactive by the rapid HIV antibody tests, even if the initial EIA results are negative.
Screening and confirmatory tests for HIV-1/-2 antibodies cannot distinguish between active neonatal HIV infection and passive transfer of maternal HIV antibodies in infants during the postnatal period (up to 18 months of age). Reactive and confirmed positive antibody test results in infants during this period may indicate passive transfer of maternal HIV antibodies. Diagnosis of HIV infection in newborns and infants up to 18 months should be made by virologic tests, such as detection of HIV-1 DNA or RNA (HIVP / HIV-1 DNA and RNA Qualitative Detection by PCR, Plasma) or HIV-1 RNA (HIVDQ / HIV-1 RNA Detection and Quantification, Plasma).
A reactive screen and confirmed HIV antibody test result should be reported by the health care provider to the State Department of Health in accordance with the legislation in some states.
Assay performance characteristics have not been established for the following specimen characteristics:
-Containing particulate matter
See HIV Serologic Interpretive Guide in Special Instructions for further interpretive information.
1. Constantine N: HIV antibody assays May 2006. In HIV InSite Knowledge Base (online textbook). Available at: http://hivinsite.ucsf.edu/InSite?page=kb-00&doc=kb-02-02-01
2. Centers for Disease Control and Prevention and Association of Public Health Laboratories. Laboratory testing for the diagnosis of HIV infection: Updated recommendations. June 27, 2014. Available from http://stacks.cdc.gov/view/cdc/23447
3. Hariri S, McKenna MT: Epidemiology of human immunodeficiency virus in the United States. Clin Microbiol Rev 2007;20:478-488
4. Owen SM, Yang C, Spira T, et al: Alternative algorithms for human immunodeficiency virus infection diagnosis using tests that are licensed in the United States. J Clin Microbiol 2008;46:1588-1595