Optimal frequency of CD4 cell count and HIV RNA monitoring prior to initiation of antiretroviral therapy in HIV-infected patients

Context: Guidelines regarding the frequency of CD4 cell count and HIV RNA monitoring in HIV-infected patients vary, with recommended strategies ranging from every 2 to every 6 months. Objective: To determine optimal CD4 cell count and HIV RNA monitoring frequency in HIV-infected patients prior to antiretroviral therapy initiation. Design: Cost-effectiveness (CE) analysis using an HIV simulation model incorporating CD4 cell count and HIV RNA as immunological and virological predictors of clinical outcomes. Setting: Hypothetical clinical setting. Patients: Simulated cohort based on initial clinical presentation of HIV-infected patients in the US. Intervention: CD4 cell count and HIV RNA monitoring at frequencies ranging from every 2 to 24 months prior to antiretroviral initiation, as well as accelerated monitoring frequencies as CD4 cell counts approach a specified treatment threshold. Outcome measures: Life expectancy, quality-adjusted life expectancy and costs. Results: For patients presenting with median CD4 cell count 546/mm(3) and median HIV RNA 4.8 log(10) copies/ml, incremental CE ratios ranged from US$37800/quality-adjusted life year (QALY) gained for a constant testing frequency of every 18 months compared with every 24 months, to US$303300/QALY gained for a constant testing frequency of every 2 months compared with every 4 months when starting treatment at a CD4 cell count of 350/mm(3). Monitoring every 12 months until a warning CD4 cell count threshold of 450/mm(3) followed by every 3 months until 350/mm(3) had an incremental CE ratio of US$74700/QALY gained. When starting antiretroviral therapy at CD4 cell count 200/mm(3), monitoring every 12 months until, 300/mm(3) followed by every 2 months until treatment initiation yielded an incremental CE ratio of US$52200/QALY gained compared with the next best strategy. Increasing monitoring frequency as CD4 cell counts approached a treatment threshold yielded greater incremental clinical benefit for less cost than strategies using a constant frequency. Conclusions: Monitoring HIV-infected patients every 12 months until 100 CD4 cells/mm(3) prior to a specified treatment threshold followed by more frequent monitoring every 2 or 3 months until antiretroviral therapy initiation is both more effective and cost-effective than the current standard of care.