How are HIV testing results confirmed?

Updated: Sep 19, 2018
  • Author: David J Cennimo, MD, FAAP, FACP, AAHIVS; Chief Editor: Michael Stuart Bronze, MD  more...
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Human immunodeficiency virus (HIV) infection is typically confirmed with Western blot. The assay involves separation of the viral proteins by molecular weight on a polyacrylamide gel. The viral proteins are then electrotransferred from the gel to a solid support. The media is incubated with the patient’s serum, and the pattern of reactivity is read. The Western blot result can be positive, negative, or indeterminate.

According to the CDC and the Association of State and Territorial Public Health Laboratory Directors [45] a Western blot result is considered positive when two of the following bands are present: gp 120/160, gp 41, or p24. A negative Western blot result is defined as the absence of all bands. The result is considered indeterminate when one or more bands are present but do not meet the criteria for a positive Western blot result.

A positive HIV-1 Western blot result following a positive EIA result for HIV-1 or HIV-2 is diagnostic of established HIV-1 infection. A negative HIV-1 Western blot result following a positive EIA result for HIV-1 or HIV-2 is considered a true negative unless acute HIV-1 infection or infection with HIV-2 is suspected.

An indeterminate Western blot result can result from true infection (eg, HIV-1 infection that has not completely seroconverted, advanced AIDS, HIV-2 infection) or no infection [46] (eg, participant in a HIV-1 vaccine trial, pregnancy, elevated bilirubin levels, hemodialysis, malignancy, autoimmune diseases). An indeterminate Western blot result should prompt repeat testing with Western blot in 2-4 weeks unless acute HIV-1 or HIV-2 infection is suspected. [40] Non-B subtypes are detected by current HIV-1 Western blots, with sensitivity and specificity equal to those for subtype B.

Other available confirmatory tests include the indirect IFA and radioimmunoprecipitation assay; however, they are infrequently used in clinical practice.

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