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suspected or repeat HIV serologic testing in 2 to 4 weeks. If no additional WB bands develop during that
time, the patient is considered not to be infected with HIV-1. An unreadable HIV-1 antibody WB result
indicates the presence of smear or blotches obscuring proper reading of the WB strip. Such findings
indicate probable nonspecific binding of antibodies in the patient's serum to the strip. For specimens with
such unreadable WB results, HIV-2 antibody test by EIA will be performed automatically (at additional
charges). See HIV Serologic Screening Algorithm (excludes HIV rapid testing) and HIV Rapid Serology
Follow-up Algorithm in Special Instructions
Reference Values:
Negative
See HIV Serologic Interpretive Guide in Special Instructions for further interpretive information.
If this test is ordered as a follow-up test on a patient with a reactive rapid HIV antibody test result,
Centers for Disease Control and Prevention (CDC) recommends supplemental testing with Western blot,
even if routine antibody screening result is negative.
Clinical References: 1. Constantine N: HIV antibody assays May 2006. In HIV InSite Knowledge
Base (online textbook) 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 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, 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
HIV-1/-2 Antibody Confirmatory Evaluation, Serum
Clinical Information: AIDS is caused by at least 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, exposure to infected blood or blood products, or
from an infected mother to her fetus or infant. HIV type 2 (HIV-2) was 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 into 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 HIV antibody tests should only be ordered for patients who are found to be
reactive by routine HIV-1/-2 antibody screening tests or by rapid HIV antibody tests. However, for testing
algorithms that begin with rapid HIV antibody tests, confirmatory antibody testing should be performed
regardless of the result of the EIA or CIA tests. Individuals at risk for HIV infection may have negative
HIV antibody screening test results by EIA or CIA with indeterminate Western blot results (especially
during early HIV infection). Such individuals may be erroneously interpreted as negative for HIV
infection, despite having reactive rapid HIV antibody test results.
Useful For: Confirmatory detection of HIV-1 and/or HIV-2 antibodies in patients with reactive
antibody screen or rapid HIV antibody results
Interpretation: An HIV-1 antibody Western blot (WB) result is interpreted as positive when at least 2
of the 3 following bands are present: p24, gp41, and gp120/160. A positive HIV-1 antibody WB result
following a reactive HIV-1/-2 antibody screening test result or reactive rapid HIV antibody test result
indicates infection with HIV-1, but it does not indicate the stage of disease. In many US states, positive
confirmatory HIV antibody test results are required to be reported to the state department of health. A
negative HIV-1 antibody WB result with either a reactive HIV-1/-2 antibody screening test or a reactive
rapid HIV antibody test, in the absence of signs, symptoms, or risk factors for HIV infection, probably
indicates a false-positive screening test or rapid test. However, a negative HIV-1 WB does not exclude the
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