CD4 and AIDS: A collaborative analysis of observational data found that deferring treatment initiation from between 351 and 450 cells/μl to between 251 and 350 cells/μl increased the hazard of AIDS or death by 28% [12], and the HPTN 052 trial found that delaying treatment until CD4 count was lower than 250 cells/μl was associated with a 41% increased hazard of adverse clinical outcome [5].