HIV-1/-2 Antibody Evaluation, Serum
Screening and confirmation of HIV-1 and/or HIV-2 infection
Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
AIDS is caused by 2 known types of HIV. HIV type 1 (HIV-1) was isolated from patients with AIDS, AIDS-related complex, and asymptomatic infected individuals at high risk for AIDS. The virus is transmitted by sexual contact, by exposure to infected blood or blood products, or from an infected mother to her fetus or infant. HIV type 2 (HIV-2) was first isolated from patients in West Africa in 1986. It appears to be endemic only in West Africa and it also has been identified in individuals who had sexual relations with individuals from that geographic region. HIV-2 is similar to HIV-1 in viral morphology, overall genomic structure, and its ability to cause AIDS.
Antibodies against HIV-1 and HIV-2 are usually not detectable until 6 to 12 weeks following exposure and are almost always detectable by 12 months. They may fall to undetectable levels in the terminal stage of AIDS.
Routine serologic screening of patients at risk for HIV-1 or HIV-2 infection usually begins with a HIV-1/-2 antibody screening test, which may be performed by various FDA-approved assays, including rapid HIV antibody tests, EIA, and chemiluminescent immunoassay (CIA) methods. In testing algorithms that begin with EIA or CIA methods, confirmatory antibody testing by Western blot assay should only be performed on specimens that are repeatedly reactive by EIA or CIA.
Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.
See HIV Serologic Interpretive Guide in Special Instructions for further interpretive information.
A reactive HIV-1/-2 antibody screening test result suggests the presence of HIV-1 and/or HIV-2 infection, but it is not diagnostic for HIV infection and should be considered preliminary. This result does not differentiate between HIV-1 and HIV-2 antibody reactivity. Confirmatory testing by HIV-1 antibody-specific Western blot (WB) or immunofluorescence assay is necessary to verify the presence of HIV-1 infection. Presence of HIV-2 infection is confirmed by supplemental testing with an HIV-2 antibody-specific line immunoassay.
All specimens that are reactive by HIV-1/-2 antibody screening test will be automatically tested by WBAR / HIV-1/-2 Antibody Confirmatory Evaluation, Serum at an additional charge. See the individual test IDs for interpretation of these subsequent test results. All initially positive confirmatory HIV antibody test results should be verified by submitting a second serum specimen for repeat testing. Positive confirmatory HIV antibody test results are required under laws in many states to be reported to the departments of health of the respective states where the patients reside.
A negative HIV-1/-2 antibody screening test result indicates the absence of HIV-1 or HIV-2 infection. However, confirmatory testing by WB (WBAR / HIV-1/-2 Antibody Confirmatory Evaluation, Serum) is necessary for specimens that are reactive by the rapid HIV antibody tests; even if the screening test results are negative.
The following algorithms are available in Special Instructions:
-HIV Rapid Serologic Testing Follow-up Algorithm
-HIV Testing Algorithm (excludes HIV rapid testing)
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
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.
This test is not indicated for screening or confirmatory testing of patients with reactive results obtained using rapid HIV antibody tests.
A reactive screening test result is not diagnostic for HIV infection and should be considered preliminary. The positive predictive value of a reactive screening test result 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 and higher the false-positive rate for the test. Diagnosis of HIV infection must be based on positive results from confirmatory or supplemental serologic or molecular tests.
Negative HIV-1/-2 antibody screening test results should be evaluated cautiously in patients with 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 screening test results are negative.
Serologic tests (screening and confirmatory) 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). Diagnosis of HIV infection in newborns and infants should be made by virologic tests such as detection of HIV RNA (HIVQU HIV-1 RNA Quantification, Plasma) or HIV proviral DNA (PHIV / HIV-1 Proviral DNA Qualitative Detection by PCR, Blood).
Performance characteristics have not been established for the following specimen characteristics:
-Individuals of <2 years of age
-Grossly hemolyzed (hemoglobin level of >500 mg/dL)
-Grossly lipemic (triolein level of >3,000 mg/dL)
-Grossly icteric (total bilirubin level of >20 mg/dL)
-Containing particulate matter
There was 100% agreement among 50 confirmed HIV-1 antibody-positive (by Western blot) and 50 HIV-1/-2 antibody screen-negative (Bio-Rad SD HIV-1/HIV-2 Plus O EIA) clinical serum specimens tested by this VITROS Anti-HIV 1+2 assay.
Testing of 1 known-negative and 3 known-positive serum specimens in duplicate over 10 assay runs showed inter-assay %CV ranging from 7.2% to 12.6% for the signal-to-cutoff (S/CO) ratios, with total agreement in the interpretive results.
Total agreement in interpretive results was observed among single aliquots of 2 known-negative and 3 known-positive (with low to high S/CO values) serum specimens (plastic screw-capped vials) tested at each of 5 freeze-thaw cycles. For 2 known-negative and 3 known-positive serum specimens stored in plastic serum gel tubes for 7 days at 2 degrees to 8 degrees C, testing on day 1, 3 and 7 of storage showed good stability (100% agreement of interpretive results) of these specimens under such condition.
Clinical Reference Provides recommendations for further in-depth reading of a clinical nature
1. Constantine N: HIV antibody assays May 2006. In HIV InSite Knowledge Base (online textbook); Available from URL: http://hivinsite.ucsf.edu/InSite?page=kb-00&doc=kb-02-02-01
2. Branson BM, Handsfield HH, Lampe MA: Center for Disease Control and Prevention: Revised recommendations for HIV testing of adults, adolescents, and pregnant women in health-care settings. MMWR Recomm Rep 2006;55:1-17
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: Alternative algorithms for human immunodeficiency virus infection diagnosis using tests that are licensed in the United States. J Clin Microbiol 2008;46:1588-1595