HIV-1/2 Antigen and Antibodies, Fourth Generation, with Reflexes – 91431

Clinical Significance

HIV-1/2 Antigen and Antibodies, Fourth Generation, with Reflexes – This test is used to help diagnose HIV-1 and HIV-2 infection, including acute infection, and to differentiate HIV-1 from HIV-2. It is consistent with the HIV diagnostic algorithm proposed by the Centers for Disease Control and Prevention [2]. It can be used in adults, including pregnant women, and in children at least 2 years old.

This test allows detection of acute HIV-1 infection based on the presence of p24 antigen, before seroconversion occurs, allowing for earlier diagnosis than with previous tests. It can also detect HIV-1 and HIV-2 post-seroconversion, based on antibodies. If the HIV-1/HIV-2 antigen/antibody test is positive, an antibody-based HIV-1/HIV-2 test is done (at additional charge) to confirm infection and identify whether it is caused by HIV-1 or HIV-2. However, the HIV-1/HIV-2 differentiation test will be negative during acute infection (prior to development of specific antibodies). If the antibody-based HIV-1/HIV-2 test is negative, the blood specimen will be reflex-tested for the presence of HIV-1 RNA (at additional charge) to identify patients with acute HIV-1 infection [1].

The United States Preventive Services Task Force (USPSTF) recommends HIV screening for all pregnant women, and for individuals between 15 and 65 years of age who live in regions with an HIV prevalence of >0.1% [2]. In addition, antigen/antibody-based HIV testing is recommended for high-risk individuals who want to begin pre-exposure prophylaxis (PrEP) therapy, because HIV-positive patients who start PrEP without knowing their HIV status face an elevated risk of antiretroviral resistance [3,4].

Because 40% of new HIV infections are transmitted unknowingly by people unaware of their HIV status, early diagnosis is important to reduce HIV transmission [5]. Antigen/antibody-based HIV screening 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].