These studies measured disease progression as a function of CD4 count, viral load, or the development of opportunistic infection, where a CD4+ cell count of less than 200 cells/μL [3], [13], [21], increased viral load [13], [21], and opportunistic infections such as tuberculosis, candidiasis, lymphadenopathy, and chronic diarrhea [22] are associated with an increased prevalence of anemia. Here, CD4 is linked to anemia (phenotype).