What is the role of viral load testing in the management of HIV infection?

Updated: Jun 23, 2020
  • Author: Philip A Chan, MD, MS; Chief Editor: John Bartlett, MD  more...
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HIV viral load testing

Among patients on antiretroviral therapy, HIV viral load is the most important marker of treatment response. All patients should have their viral load measured at diagnosis and regularly thereafter. Increased or detectable viral loads in a patient on antiretroviral therapy indicates either nonadherence (most common) or development of drug resistance.

HIV replication occurs primarily in lymphoid tissue, but high levels of viremia can be detected in infected individuals. Early studies made it clear that the level of viremia at the "set point" (ie, after acute infection, but prior to significant immune decline) was associated with the rate of CD4 cell loss and hence the time to AIDS and death. [19, 20] One analogy is that, if the CD4 cell count can be thought of as how far a train is from the end of the line, the viral load is a measure of how fast the train is going.

Viral load can be considered a quantitative measure of viral RNA genomes in the peripheral circulation. The most common assays involve reverse transcription to convert viral RNA (which is readily destroyed by ubiquitous RNAses) to more easily manipulated DNA. After reverse transcription, the laboratory uses one of various amplification techniques that have been developed to provide a quantitative measure of the DNA. [33] Most rely on some form of nucleic acid amplification such as polymerase chain reaction (PCR). Internal standards of amplification targets of known concentration are compared to patient specimens in order to provide quantitation of viral load. Because nucleic acid amplification techniques are incredibly sensitive, it is crucial to avoid contamination of specimens in the laboratory. Not only is the specific quantitative analysis of viral load important in clinical management, but qualitative viral load tests are used in screening of blood donations.

An optimal response to treatment would be a reduction in the viral load to undetectable levels (for most assays, this equates to levels of less than 20 copies/mL, but this may vary). An occasional "blip" may occur; these are typically below 400 copies/mL and are not predictive of virologic failure. [34] For the purpose of monitoring therapy, virologic failure is defined as a confirmed viral load in excess of 200 copies/mL. [16] In general, HIV viral load testing should be performed every 3-6 months in people living with HIV infection.

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