What indicates the diagnosis of AIDS?

The diagnosis of AIDS (Acquired Immunodeficiency Syndrome) is indicated by a CD4 count less than 200 cells/mm³. This threshold is significant because CD4 cells are a type of white blood cell that play a critical role in the immune system, and their reduction indicates a severely compromised immune response. When the CD4 count falls below this level, the individual is considered to be at very high risk for opportunistic infections and other illnesses as their immune system is severely weakened.

While the presence of opportunistic infections is also a defining characteristic of AIDS, it is often considered as a result of the immunocompromised state indicated by the low CD4 count. Thus, even in the absence of opportunistic infections, a CD4 count below 200 is sufficient to make the diagnosis of AIDS.

In contrast, a CD4 count greater than 200 suggests that the immune system is still functioning reasonably well, and therefore does not indicate AIDS. The presence of a high HIV viral load could also be a concern in managing HIV infection, but it is not directly used as a criterion for diagnosing AIDS on its own.