In this instance, CD4 testing informs the prioritising of ART initiation in patients with a CD4 ≤ 350 cells/μL, and determines the need for opportunistic infection prophylaxis (at a CD4 count of ≤200 cells/μL) and for testing for cryptococcal antigenaemia (at a CD4 count of ≤100 cells/μL) [6]. This evidence concerns the gene CD4 and Opportunistic infection.