HIV-1/2 antigen/antibody immunoassay testing is performed in combination with HIV-1/2 antibody differentiation immunoassay in a patient with a suspected HIV infection. A negative result indicates an HIV infection is not present and no further testing is needed. Immunosorbent assay (ELISA) may be used as the initial test for determining HIV. However, fourth-generation HIV-1/2 antigen/antibody immunoassay testing is able to determine HIV p24 antigen as well as HIV antibodies, unlike third-generation ELISA testing which only determines HIV antibodies.
HIV-1/2 antibody differentiation immunoassay testing confirms a positive HIV-1/2 antigen/antibody immunoassay and determines if a patient has HIV-1, HIV-2, or both. The antibody differentiation assay is preferred over Western blot for confirmatory testing which has been used in the past to confirm a positive ELISA test.
If the HIV-1/2 antibody/antigen immunoassay is positive and the HIV-1/2 antibody differentiation immunoassay is inconclusive, a nucleic acid testing (NAT) is performed. A negative NAT test in the setting of inconclusive HIV-1/2 antibody immunoassay indicates a false positive HIV-1/2 antibody/antigen immunoassay.
Viral load testing is used to determine the amount of RNA in the patient's plasma. The level of the patient's viral load helps determine the progression of HIV and effectiveness of therapy for HIV (refer to the Picmonic on "HIV Stages"). If the patient's viral load is considered "undetectable," the test is unable to report the viral load but does not indicate the virus has been eliminated.
A pregnant woman with HIV infection may transplacentally transmit the virus to the newborn. The polymerase chain reaction (PCR) test is performed on a neonate’s blood whose mother has an HIV infection in order to determine the presence of HIV-1 DNA. This test differentiates between the mother's HIV antibodies and the actual presence of HIV-1 DNA in the newborn.
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