Anti-retroviral therapy for HIV: who should we test and who should we   treat?
  In most countries CD4+ cell counts are still used for deciding when to start HIV-positive people on anti-retroviral therapy. However, various CD4+ thresholds, 200, 350 or 500/\muL, are chosen arbitrarily and for historical reasons. Here we consider the optimal CD4+ threshold at which asymptomatic HIV-positive people living in Botswana, South Africa and Zimbabwe should start treatment depending on their prognosis given their CD4+ cell counts or viral load. We also examine the optimal interval at which people should be retested if they are HIV-negative. This analysis shows that while the use of CD4+ cell counts or viral load tests could have been useful in deciding how to triage patients for treatment at the start of the epidemic this is no longer the case except possibly for those aged about 15 to 25 years. In order not to do harm to individual patients everyone should be started on ART as soon as they are found to be HIV-positive. 
Brian G. Williams, Renier van Rooyen and Martin Nieuwoudt
q-bio.QM stat.AP