What defines an AIDS cell count?

The defining criterion for an AIDS diagnosis is based on the measurement of CD4 T-lymphocyte (or CD4 cell) counts in a patient living with HIV. A count of less than 200 cells/mm³ indicates severe immune system compromise and qualifies for an AIDS diagnosis. This low level of CD4 cells suggests that the immune system is significantly weakened, making the individual more susceptible to opportunistic infections and certain cancers, which are hallmark conditions associated with AIDS.

In contrast, higher CD4 counts do not indicate AIDS; counts in the range of 200 to 499 cells/mm³ represent a less severe immune system impairment, and counts above 500 cells/mm³ suggest a relatively healthy immune function. Thus, the distinction in these counts is critical for proper diagnosis and treatment planning in patients infected with HIV.