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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.
The following algorithm is available in Special Instructions:
-HIV Testing Algorithm (Fourth Generation Screening Assay) Including Follow-up of Reactive HIV Rapid Serologic Test Results
Detection of HIV-1 and/or HIV-2 antibodies in cadaveric or hemolyzed serum specimens from nonsymptomatic patients with or without risk factors for HIV infection. This assay 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. Confirmatory testing by HIV-1/-2 antibody differentiation or HIV-1 specific Western blot (WB) assay is necessary to verify the presence of HIV-1 infection. The presence of HIV-2 infection is screened by HIV-2 antibody-specific EIA with confirmation by HIV-2 antibody-specific immunoblot assay.
All EIA-reactive specimens tested will automatically be tested by HIVDI / HIV-1 and HIV-2 Antibody Differentiation, Serum at an additional charge. Please see the individual unit code for interpretation of these subsequent test results. 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 indicates the absence of HIV-1 or HIV-2 infection. However, confirmatory testing by WB (HV1WB / HIV-1 Antibody Confirmation by Western Blot, Serum) is recommended for specimens that are reactive by the rapid HIV antibody tests, even if the EIA results are negative.
Reflex tests have not been FDA-approved for testing on cadaveric specimens.
This test is not offered as a screening or confirmatory test for blood donor specimens.
This test is not offered for maternal/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 by Western blot 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.
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 URL: http://hivinsite.ucsf.edu/InSite?page=kb-00&doc=kb-02-02-01
2. Centers for Disease Control and Prevention: Revised recommendations for HIV testing of adults, adolescents, and pregnant women in health-care settings. MMWR Morb Mortal Wkly Rep 2006;55(RR14):1-17
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