The characteristic laboratory finding in HIV infection is:

The characteristic laboratory finding in HIV infection is:

• A. decreased numbers of CD8 T cells.
• B. decreased numbers of CD4 T cells.
• C. decreased numbers of CD20 B cells.
• D. decreased immunoglobulins.

Answer: (B)

HIV directly targets CD4+ T helper cells, so the hallmark laboratory finding is a progressive loss of these CD4 T cells. As the infection advances, the CD4 count declines, and when it falls below about 200 cells per microliter, AIDS defining immunodeficiency is reached. This depletion explains the vulnerability to opportunistic infections. Often the CD4:CD8 ratio becomes inverted because CD8 T cells are relatively preserved or even increased. B cells (CD20) are not characteristically decreased in HIV; in fact, immunoglobulin levels can be elevated due to polyclonal B cell activation, with impaired specific antibody responses. So the key lab feature is the reduced CD4 T cell count.

HIV directly targets CD4+ T helper cells, so the hallmark laboratory finding is a progressive loss of these CD4 T cells. As the infection advances, the CD4 count declines, and when it falls below about 200 cells per microliter, AIDS defining immunodeficiency is reached. This depletion explains the vulnerability to opportunistic infections. Often the CD4:CD8 ratio becomes inverted because CD8 T cells are relatively preserved or even increased. B cells (CD20) are not characteristically decreased in HIV; in fact, immunoglobulin levels can be elevated due to polyclonal B cell activation, with impaired specific antibody responses. So the key lab feature is the reduced CD4 T cell count.