Which lab assays are used to accurately diagnose early HIV infection?

Updated: Jun 23, 2020
  • Author: Philip A Chan, MD, MS; Chief Editor: John Bartlett, MD  more...
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A key feature of HIV infection is the prolonged clinical latency that occurs prior to significant immune deficiency. [5, 6, 7, 8, 9] During this period, which is highly variable but generally lasts several years from the time of initial infection, the individual may exhibit few or no symptoms but is still able to transmit the infection to others. Early detection is important to minimize these risks.

Accurate diagnosis of HIV infection has evolved over time and has historically relied on detection of antibodies specific to HIV-1 or HIV-2 infection. The period immediately following HIV infection, before the development of antibodies, is the “window period” during which an antibody test result may be negative. Newer fourth-generation HIV tests combine antibody and antigen detection. These combination immunoassays allow earlier HIV detection, as they detect both HIV-1 and HIV-2 antibodies, as well as HIV-1 p24 antigen. [10] The p24 antigen is a viral capsid protein that arises in early infection, before development of HIV antibodies.

Importantly, clinicians should be aware that HIV testing should include assays that are specific for both HIV-1 and HIV-2. Most worldwide HIV infections are due to HIV-1. HIV-2 should be considered in individuals from West Africa or in persons with sex partners from West Africa. Some HIV antibody tests are specific only for HIV-1 antibodies. HIV-2 should also be considered in people with clinical evidence of HIV infection who are HIV-1–negative or have indeterminate testing results. Monitoring HIV-2 infection is difficult, as available viral load testing is specific for HIV-1.

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