Virus Load Testing

Clinical Utility of Plasma HIV-1 RNA Monitoring

Numerous studies have demonstrated the correlation of plasma HIV-1 RNA levels with stage of disease. Patients with AIDS or symptomatic HIV infection have significantly higher titers of plasma HIV-1 RNA than do those with asymptomatic infection. In addition, patients with higher virus loads are likely to progress more rapidly than patients with lower virus loads. For example, individuals with plasma HIV-1 RNA levels >100,000 copies/mL within six months of seroconversion are 10-times more likely to progress to AIDS within five years than patients with lower levels of plasma HIV-1 RNA (49). Plasma HIV-1 RNA levels are correlated with the rate of CD4 count decline and with the rates of progression to AIDS and death in untreated patients with established HIV-1 infection (50) (Table 4).

Most studies suggest that plasma HIV-1 RNA levels provide prognostic information even in late stages of disease (51). Similar results have been observed in children with perinatally acquired HIV-1 infection (52; 53). However, some studies suggest that the CD4 count is a better predictor of disease progression than is plasma HIV-1 RNA in patients with very low CD4 counts (below 50 cells/mm3) (54).

The rapid change in plasma HIV-1 RNA levels in response to treatment makes it possible to assess the effectiveness of antiviral therapy within a matter of weeks. The relationship between change in virus load and treatment benefit has been analyzed in several large clinical trials (55). These studies show that a decrease in plasma HIV-1 RNA confers a significant reduction in risk of disease progression, independent of baseline plasma HIV-1 RNA level and CD4 count, and independent of the increase in CD4 count due to treatment (56). Much of the benefit of antiretroviral therapy can be attributed to its effect on plasma HIV-1 RNA levels. A 0.3-log10 (2-fold) reduction in plasma HIV-1 RNA levels confers a 30% reduction in the risk of progression to AIDS or death (57); a 1-log10 (10-fold) reduction reduces the risk of disease progression by approximately two-thirds (58). Although initial studies suggested that HIV-1 RNA was a stronger predictor of response to antiretroviral therapy than the change in CD4 count, subsequent studies make clear the prognostic importance of improvement in both markers (59; 60).

4/15/01

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