CD4 and substance abuse: The study cohort consisted of 57 HIV subjects with advanced disease (CD4 nadir <300; median, 61 cells/μl; range, 1–261 cells/μl), relatively low CD4 counts (median, 81 cells/μl; range, 3 – 688 cells/μl), variable plasma HIV RNA levels (median 2,460 copies/ml; range, undetectable – 2,210,000 copies/ml), and high frequency of recent substance abuse (70%) and HCV co-infection (47%) (Table 1).