Cohort studies indicate that starting highly active antiretroviral therapy (HAART) when the CD4+ T-cell count is less than 200 cells/muL is associated with poor outcomes. These studies have been unable to address how early HAART should be initiated, however. This report uses a modeling approach to compare starting HAART at a mean CD4+ T-cell count greater than 350 cells/microL (early) versus less than 350 cells/microL but greater than 200 cells/microL (later).
A Markov model tracks people with HIV infection through 6 disease stages defined by CD4+ T-cell count ranges over a 25-year period. Transition probabilities between the disease stages for 6-month periods vary according to initial viral load. Sequences of different first-line, second-line, and "salvage" antiretroviral regimens are defined, and their impact on transition probabilities is estimated. HAART effectiveness is based on data from an urban hospital-based HIV clinic, supplemented by clinical trial data. The model computes the incremental cost-effectiveness of alternative treatment patterns and includes sensitivity analyses for a range of plausible alternative input values.
Starting HAART earlier rather than later increases total lifetime costs by $19,074, increases years of life by 1.21 years, increases discounted quality-adjusted life-years by 0.61, and has an incremental cost-effectiveness ratio of $31,266 per quality-adjusted life-year. Early therapy is more cost-effective when the impact of HAART on well-being is smaller.
Initiation of HAART at a CD4+ T-cell count greater than 350 cells/microL may be cost-effective (less than $50,000 per quality-adjusted life-year) compared with initiating HAART at a CD4+ T-cell count less than 350 cells/microL but greater than 200 cells/muL and may result in longer quality-adjusted survival.