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Use of HIV Viral Load in Clinical Practice: Back to the Future
- Michael S. Saag, MD
- The University of Alabama at Birmingham, Birmingham, AL 35294-2050 Requests for Reprints: Michael S. Saag, MD, The University of Alabama at Birmingham, 908 20th Street South, CCB #178, Birmingham, AL 35294-2050.
The motion picture Back to the Future, Part III contains a famous scene in which the protagonist, Marty McFly, must propel a makeshift 1880s steam locomotive down a stretch of railroad track toward a ravine where the bridge has collapsed. To get “back to the future,” Marty must accelerate the locomotive to a speed of 88 miles per hour before the track ends and he tumbles into the abyss. The natural history of human immunodeficiency virus (HIV) infection in individual patients is much like the image of a runaway train heading down a limited stretch of track toward an ill-defined demise [1]. The CD4+ cell count, which has been the best marker of the immediate risk for disease progression, represents the mile marker along the track that indicates the relative distance to the ravine. The HIV viral load represents the speed at which the train is moving down the track. Although each of these markers conveys important and distinct information, clinicians have been uncertain about how best to use these markers together in practice. In this issue, three articles help elucidate the respective roles played by viral load and CD4+ cell counts as represented by the train in Back to the Future.
Historically, CD4+ cell counts were first recognized as prognostic indicators of the short-term risk for the development of new opportunistic infections or death, yet their ability to predict disease progression over a more prolonged period of time was limited. In the early 1990s, new technologies, including quantitative reverse transcriptase polymerase chain reaction (PCR) [2, 3], branched DNA (bDNA) [4], and nucleic acid sequence-based assay (NASBA) techniques [5], allowed accurate measurement of virally associated circulating HIV RNA in plasma. The amount of HIV RNA detected is directly related to the production of HIV in tissue …
