Prior studies have found that DLco impairment (with or without normal spirometry) among PWH is associated with higher HIV RNA levels, CD4<200 cells/μl, and lower nadir CD4 cell count, as well as a history of bacterial pneumonia, Pneumocystis pneumonia, cocaine use, and positive hepatitis C RNA [4, 7–9, 38–42]. This evidence concerns the gene CD4 and pneumocystosis.