What CD4 count threshold defines AIDS (an AIDS-defining level)?

What CD4 count threshold defines AIDS (an AIDS-defining level)?

• A. <50
• B. <200
• C. <500
• D. <1000

Answer: (B)

CD4+ T cells are the immune system’s main line of defense against opportunistic infections. In HIV infection, their numbers steadily fall, and AIDS is defined when the immune system becomes severely compromised. The classic cutoff is a CD4 count below 200 cells per microliter, which marks a level where the risk of opportunistic infections—such as Pneumocystis jirovecii pneumonia and esophageal candidiasis—soars. That threshold is the standard criterion used to categorize AIDS. It’s also important to know that AIDS can be diagnosed if a person has an AIDS-defining illness regardless of the CD4 count. Normal CD4 counts are roughly 500–1500 cells/µL, so counts well above 200 do not define AIDS by themselves.

CD4+ T cells are the immune system’s main line of defense against opportunistic infections. In HIV infection, their numbers steadily fall, and AIDS is defined when the immune system becomes severely compromised. The classic cutoff is a CD4 count below 200 cells per microliter, which marks a level where the risk of opportunistic infections—such as Pneumocystis jirovecii pneumonia and esophageal candidiasis—soars. That threshold is the standard criterion used to categorize AIDS. It’s also important to know that AIDS can be diagnosed if a person has an AIDS-defining illness regardless of the CD4 count. Normal CD4 counts are roughly 500–1500 cells/µL, so counts well above 200 do not define AIDS by themselves.