What is one of the criteria for diagnosing AIDS?

A key criterion for diagnosing AIDS is a CD4 count of less than 200 cells/mm³. This threshold indicates a significant compromise in the immune system due to HIV infection, leading to an increased risk for opportunistic infections and certain cancers. When the CD4 count drops below this level, it suggests that the body is unable to effectively combat infections and increases the severity of the condition, justifying the AIDS diagnosis.

In contrast, while a CD4 count less than 300 could indicate a weakened immune response, it does not meet the specific criteria for an AIDS diagnosis. A positive viral load indicates active viral replication but is not a sole criterion for diagnosing AIDS. Similarly, a CD4 percentage less than 30% also indicates immune compromise but is not the standard definitive criterion used in the AIDS diagnosis context. Therefore, the identification of a CD4 count below 200 is the critical metric for diagnosing AIDS.