![]() At the point-of-care, other options for testing can be performed on oral secretions or finger-stick samples. Testing for HIV is ideally performed with a combination antigen/antibody immunoassay, which requires a blood draw. ![]() The old way of testing HIV: 1) HIV Abs by ELISA w/ 2) confirmation by Western blot or detectable plasma HIV RNA (some places may still use this method. Other FDA–approved tests for detection and confirmation of HIV infection include combination tests (for p24 antigen and HIV antibodies) and qualitative HIV-1 RNA.” AAFP The sensitivity and specificity of the rapid test are also both greater than 99.5% however, initial positive results require confirmation with conventional methods. Rapid HIV testing may use blood or oral fluid specimens and can provide results in five to 40 minutes. The test is highly accurate (sensitivity and specificity greater than 99.5%), and results are available within one to two days from most commercial laboratories. The conventional serum test for diagnosing HIV infection is the repeatedly reactive immunoassay followed by confirmatory Western blot or immunofluorescent assay. Specimens that do not confirm positive by Multispot may require further analysis by HIV RNA PCR.CDC guide on testing for HIV. Specimens that are reactive by initial HIV-1/HIV-2 antibody immunoassay should be confirmed by Multispot testing. This confirmation immunoassay, also known as Multispot, detects seroconversion earlier than Western blot and eliminates most indeterminate results that occur due to nonspecific reactivity from alloantibodies. The follow-up confirmation test for reactive results is a new HIV-1/HIV-2 differentiation immunoassay. The first test in the new algorithm remains the combination HIV-1/HIV-2 antibody immunoassay. Therefore, CDC and Clinical Laboratory Standards Institute (CLSI) have designed a new HIV testing algorithm that eliminates Western blot confirmation. Third generation HIV-antibody immunoassays can detect seroconversion as early as 22 days after infection, while Western blot may not show reactivity until 4 weeks or more. Improvements in sensitivity of newer generation HIV-antibody screens have created the dilemma of falsely-negative Western blot assays. Persons with stable indeterminate patterns lasting 6 months or more, in the absence of known risk factors and clinical symptoms, may be considered negative for HIV-1 antibodies. Most seroconversions will be detected in repeat Western blots within 3 months. These individuals should be further evaluated by HIV RNA PCR testing and follow-up HIV serologic testing. Individuals with a positive Western blot lacking the p31 band should be counseled that, although they may be infected, uncertainty exists about this conclusion. The complete medical history must be considered in interpreting indeterminate Western blots. Indeterminate patterns may be either false positives or early seroconverters. The majority of indeterminate patterns consist of p17, p24, or p55 alone, or combinations of these 3 bands. Presence of any 2 bands p24, gp41, gp120/160 ![]() The criteria established by the Centers for Disease Control and the Association of State and Territorial Public Health Laboratory Directors for interpretation of Western blots are as follows: In some cases, reactions with gp120 and gp160 may be due to antibodies binding to multimers of gp41. Anti-p31 also diminishes, but not to the same extent as anti-p24. Antibodies to p24 and p55 decline after the onset of symptoms, while antibodies to envelope glycoproteins persist. ![]() The earliest antibodies to appear are directed against gp160, gp120, p24, and p17, followed shortly by antibodies to gp41, p55, p66, and p51. A consistent sequence of antibody responses occurs after infection. ![]()
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