HIV Diagnostic and Molecular Testing

Rationale for approaching the virological diagnosis of HIV infection

HIV 1 & 2 Antibody Screen

Antibodies to HIV-1 and HIV-2 are detected by enzyme immunoassay (EIA). Reactive results are confirmed by HIV-1 Western blot. The HIV Western blot identifies antibodies against eight HIV-1 encoded proteins: p18, p24, p31, gp41, p51, p55, p65/66, gp120/p160. Criteria accepted by CDC/ASTPHLD are used for determining a positive HIV Western blot. These criteria require antibodies against any two of the following HIV-1 proteins: p24, gp41, gp120/160. Specimens showing reactivity to HIV-1 protein(s), but not fulfilling the criteria for a positive result, are reported as Indeterminate. All indeterminate Western blots are further tested in supplemental HIV-1 and HIV-2 specific assays. Specimens showing reactivity to non HIV-1 proteins are not assigned an indeterminate status but are instead reported as “Antibody to non-HIV-1 encoded proteins”. A negative Western blot has no detectable bands, i.e. no antibodies reacting to either HIV-1 or non-HIV-1 proteins. Supplemental assays are performed on EIA-reactive specimens which do not confirm by HIV-1 Western blot. Specimens may be forwarded, upon request, for HIV-2 specific Western blot if supplemental assays indicate HIV-2 antibodies may be present. HIV-1 and -2 EIA screens are run daily, Monday through Friday. HIV-1 Western blot confirmation assays are run on Tuesday, Thursday and Friday.

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HIV-1 RNA Quantitation

Quantitation of HIV RNA copy number is available to monitor antiviral therapy and to predict disease progression in HIV infected persons. HIV RNA quantitation may be useful to indicate when an HIV infected person should start anti-retroviral therapy and when such therapy should be adjusted. (Alone, this assay is not recommended nor approved for diagnosing HIV infection. However, in conjunction with a positive DNA PCR or a reactive EIA, the RNA quantitation may be diagnostic.) High levels of RNA are found during acute infection and in patients who are more likely to have disease progression. Inhibition of cell-free HIV, as reflected by RNA copy number, is associated with better CD4 response and clinical response in some patient populations.

To quantify HIV RNA, the UW Clinical Retrovirology Laboratory uses a real-time reverse transcription (RT)-polymerase chain reaction (PCR) amplification platform with enhanced sensitivity and broader dynamic range compared to available commercial assays. The Real-time RT-PCR assay for HIV RNA quantification has been validated against the commercial bDNA and ultrasensitive (US) RT-PCR assays.

*The dynamic range for HIV RNA detection by Real-Time RT-PCR is 30 to 1,000,000 copies/mL of plasma.

HIV clade B is the predominant virus causing HIV/AIDS in North America and Europe. To provide HIV RNA quantification for non-clade B viruses, the Roche Monitorª US-RT-PCR version 1.5 assay should be ordered.

*The dynamic range for HIV RNA quantitation by US-RT-PCR is 50 to 100,000 copies/mL of plasma.

See HIV-1 RNA Quant by Real Time in the Online Guide to Lab Testing.

HIV-2 RNA Quantitation

The Retrovirology Laboratory within the University of Washington Department of Laboratory Medicine offers a new algorithm for the laboratory diagnosis of HIV using a fourth generation HIV screening assay (Abbott Architect HIV Ag/Ab Combo Assay) and an HIV-1/-2 differentiation assay (Bio-Rad Multispot HIV-1/HIV-2 Rapid Test) to confirm the presence of HIV-1 or/and HIV-2 antibodies.  Acute HIV-1 infections are confirmed with the HIV-1 RNA assay (Abbott RealTime HIV-1 assay).  HIV-1 RNA and HIV-2 RNA assays are offered to confirm HIV-1 or/and HIV-2 infections for patient samples with undifferentiated HIV antibody status and to monitor antiretroviral therapy.

The HIV-2 RNA Quantitative Viral Load assay (HIV2VL) was developed and validated according to the Clinical and Laboratory Standards Institute (CLSI) guidelines. Recommended samples include plasma (EDTA) and CSF. The HIV2VL has successfully tested patients’ samples nationwide and from Canada since 2011.

See HIV-2 RNA Quantitative Viral Load assay in the online test guide.

HIV-1 Proviral DNA Detection

The detection of cell associated Human Immunodeficiency Proviral DNA by polymerase chain reaction (PCR) amplification is one of the most sensitive non-serologic methods for confirming HIV infection. In addition to HIV culture, this assay is recommended for confirming HIV infection in the neonate. HIV DNA PCR may also be used as a supplemental test to determine the significance of an indeterminate HIV Western Blot serology result. This test is temporarily being referred to Quest Diagnostics.

See HIV-1 Proviral DNA by PCR in the Online Guide to Lab Testing.

HIV-1 Genotypic Resistance Assay

This assay is performed once a week and an interpretive report is sent (see example of PDF document linked below). The assay involves sequencing of the HIV pol gene, after which mutations in the gene can be compared to sequences known to confer resistance to different classes of antiretroviral drugs. The assay is most useful in patients who lose viral suppression on antiretroviral therapy and should be performed before switches in therapy are entertained. Specimen requirement is a 10 mL EDTA tube at room temperature or frozen plasma at -70°C, shipped on dry ice, is also acceptable.

See HIV Genotypic Resistance Assay in the Online Guide to Lab Testing.