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Background:  CD4 percentage has been used anecdotally as a means of determining when to begin HAART, but its prognostic value in terms of patient survival has not been established in a large prospective study. This study was designed to determine whether HIV disease progression is predicted by the initial CD4 percentage, and to determine the utility of CD4 percentage as a prognostic factor in a sub-group of AIDS-free individuals with baseline CD4 cell counts between 200 and 350 cells/ µL.

Methods:  Participants who initiated triple combination therapy between August 1, 1996 and June 30, 2002 were enrolled in a population-based cohort of antiretroviral therapy-naïve HIV-positive individuals 18 years or older in British Columbia, Canada. Subjects were followed until death or June 30, 2003. The primary endpoint was non-accidental mortality, which was determined through a data linkage with the provincial vital statistics registry. Cox-proportional hazard regression was used to model the simultaneous effect of prognostic variables on survival.

Results:  A total of 1623 participants aged 18 years were included in the main analysis. When combined in a multivariate model including age, adherence to therapy, initial HIV RNA level, and a previous diagnosis of AIDS, a low CD4 percentage remained a highly significant predictor of eventual death (CD4% < 5, RR = 4.46, 95% CI 2.92 to 6.79; CD4% 5 to 14, RR = 2.43; 95% CI 1.75 to 3.38) when compared with those subjects with initial CD4 fraction of 15% or greater. However, absolute CD4 count strata had higher relative risks associated with mortality (absolute CD4 < 50/mL, RR = 6.07, 95% CI 4.11 to 8.97; 50 to 199/mL, RR = 2.95, 95% CI 2.08 to 4.18, relative to counts ≥ 200/ mL). In the sub-group analysis of 417 participants without AIDS at baseline and CD4 cell counts between 200 and 350 cells/µL, baseline CD4 fraction below 15% (RR = 2.71, 95% CI 1.20 to 6.10) and low adherence to therapy (RR = 1.18, 95% CI 1.05 to 1.33) were associated with an increased risk of death. HIV RNA levels ≥ 100 000 copies/mL were also marginally associated with mortality (RR = 2.57, 95% CI 1.00 to 6.58).

Conclusions:  These data demonstrate that CD4 percentages below 15% are independent predictors of mortality in AIDS-free patients starting HAART with CD4 cell counts between 200 and 350 cells/µL and suggest that CD4 percentage should be considered for inclusion in therapeutic guidelines used to determine when to start therapy.

Keywords: prognosis; CD4 percentage; CD4 counts