The value of the CD4+ count of 500 cells/microliters.

The CD4+ cell count is a surrogate marker used for evaluating the efficacy of therapies for HIV infection and for estimating the prognosis of patients with HIV infection. However, there is no single CD4+ count that can be used to indicate likely clinical outcome or the optimal time of treatment initiation. Protocol 019 of the AIDS Clinical Trials Group (ACTG) investigated the efficacy of zidovudine monotherapy in asymptomatic patients with HIV infection. Following results showing zidovudine to be significantly more effective than placebo in delaying the progression to AIDS in HIV-infected patients with CD4+ counts < 500 cells/microliters, further analysis of data from this trial showed that immediate zidovudine significantly delayed the time to reach a CD4+ count of 500 cells/microliters in patients with > 500 cells/microliters compared with deferred therapy. However, there was no additional advantage in terms of delayed onset of AIDS or death compared with deferred treatment. Based on the available evidence, our group believes that the threshold for initiating zidovudine monotherapy should be a CD4+ count of 500 cells/microliters. However, we also strongly advocate additional research to confirm the value of early treatment with zidovudine in asymptomatic patients. Continuing educational and collaborative research efforts will further clarify optimal therapeutic strategies in asymptomatic patients with HIV infection.