CD4 and mitochondrial DNA depletion syndrome 4a: The pooled prevalence of ADH among ART-naïve patients was significantly higher among studies that used the WHO clinical staging system to assess AHD, 58.8% (95% CI 58.8–76.0%, n = 9), compared with a pooled prevalence of AHD estimate in 44 studies that used CD4 count criteria; 40.5% (95% CI 37.0% to 44.1, n = 44), Fig. 4.