HIV-1/2 Antigen and Antibodies, Fourth Generation, With Reflexes

Test Code:   91431
This test will be available March 27, 2014.
Clinical Use:
·     Screen for and confirm HIV-1/HIV-2 infection, including acute infection
·     Differentiate HIV-1 from HIV-2 infection
Clinical Background:
More than 1.1 million people in the United States are living with HIV infection, and almost 1 in 6 (15.8%) are unaware of their infection.1 Another 50,000 individuals are newly infected.2   Identification and treatment of HIV infection can lead to substantial benefits in terms of decreased transmission, morbidity, and death.3 Center for Disease Control (CDC) recommends that all persons between the ages of 13-64 years be screened for HIV in healthcare settings located in areas where the prevalence of undiagnosed HIV infection is >0.1%, and that persons with increased risk for HIV be retested at least annually. 2 In April 2013, the U.S. Preventative Services Task Force (USPSTF) updated its 2005 guidelines on HIV screening, to recommend that clinicians screen all persons aged 15-65 years for HIV infection at least once regardless of their risk; that younger adolescents and older adults with increased risk be screened more frequently. 2 The USPSTF concurs with the CDC’s recommendation of voluntary, opt-out screening for HIV.3 The importance of detecting HIV during the acute phase (before seroconversion) is increasingly recognized; although brief, acute infection is marked by high viral load and appears to contribute dispro- portionately to transmission.4
The current HIV testing algorithm begins with a “third-generation” HIV-1/HIV-2 antibody immunoassay, followed by supplemental testing (e.g., Western blot) to confirm repeatedly reactive results. This approach is highly sensitive and specific but has several drawbacks. It cannot detect acute infection and it does not readily differentiate between HIV-1 and HIV-2. It can also cause a delay in diagnosis because, during early seroconversion, negative or indeterminate results have been obtained on Western blots. An alternative algorithm proposed by the CDC and adopted by the Clinical Laboratory Standards Institute (CLSI) is designed to avoid these drawbacks.5
The alternative algorithm begins with (preferably) a “fourth-generation” combination immunoassay that detects HIV p24 antigen in addition to HIV antibodies.  The ability to detect the p24 antigen prior to seroconversion can result in detecting HIV during acute infection. The inclusion of HIV-1/HIV-2 antibodies in the fourth generation assay will also allow the detection of HIV after seroconversion, when p24 antigen becomes undetectable. Fourth-generation assays have >99.7% sensitivity and >99.3% specificity for HIV infection and can identify most (>80%) acute infections that would otherwise require nucleic acid testing for detection.6,7 In general, they can detect infections 0 to 20 days (median, 5-7 days) before third-generation immunoassays.5,8,9
Repeatedly reactive results on fourth-generation screening tests require confirmation with a supplemental test, such as an HIV-1/HIV-2 antibody differentiation assay (e.g., MultiSpot). Differentiation between HIV-1 and HIV-2 antibodies can have treatment implications, as HIV-2 does not respond to some antiretroviral agents. Differentiation tests also tend to detect antibodies earlier than Western blots.10 Like the Western blot, HIV-1/HIV-2 antibody differentiation tests do not detect acute infection. Therefore, testing for HIV RNA is needed to resolve infection status in patients with reactive results with the fourth-generation immunoassay and negative results on the antibody differentiation test.
Individuals Suitable for Testing


·        Pregnant women
·        Adolescents and adults 15 to 65 years of age, and beyond this range for those at increased risk
·        Individuals with recent confirmed or suspected exposure to HIV-1 or HIV-2 infection
·        Children 2 years of age or older with suspected HIV infection


          Reference Range


§  Nonreactive
1.    Center for Disease Control and Prevention. HIV in the United States: At A Glance. Available at November 2013.
2.    CDC. Revised recommendations for HIV testing of adult, adolescents, and pregnant women in healthcare settings. MMWR 2006:55(No. RR-13).
3.    Moyer VA, U.S. Preventative Services Task Force. Screening for HIV: U.S. Prevention Services Task   Force Recommendation Statement: Ann Intern Med. 2013;159:51-60
4.    Detection of acute HIV infection in two evaluations of a new HIV diagnostic testing algorithm-United States, 2011-2013. MMWR 2013;62:489-494.
5.    CLSI. Criteria for Laboratory Testing and Diagnosis of Human Immunodeficiency Virus Infection;   Approved Guideline. M53-A ed. Wayne, PA: Clinical and Laboratory Standards Institute; 2011.
6.    Nasrullah M, Wesolowski LG, Meyer WA, III, et al. Performance of a fourth-generation HIV screening assay and an alternative HIV diagnostic testing algorithm. AIDS. 2013;27:731-737.
7.    Chavez p, Wesolowski L, Patel P, et al. Evaluation of Performance of the Abbott ARCHITECT HIV Ag/AB Combo Assay. J. Clin Virol. 2011;52(suppl 1):S51-S55.
8.    Fiebig EW, Wright DJ, Rawal BD, et al. Dynamics of HIV viremia and antibody seroconversion in plasma donors: implications for diagnosis and staging of primary HIV infection. AIDS. 2003;17:1871-1879.
9.    ARCHITECT HIV Ag/Ab Combo package insert. April 2012.
10.    Wesolowski LG, Delaney KP, Meyer WA, III et al. Use of Rapid HIV assays as supplemental tests in   specimens with repeatedly reactive screening immunoassay results not confirmed by HIV-1 Western blot.  J. Clin Virol.. 2013;58(1):240-244.










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