What is the CD4 count that is indicative of AIDS?

A CD4 count of less than 200 is indicative of AIDS (Acquired Immunodeficiency Syndrome). The CD4 count is a critical measure used to assess the health of the immune system in individuals infected with HIV (Human Immunodeficiency Virus). Essentially, CD4 cells are a type of white blood cell that plays an essential role in the immune response; therefore, their count is an important indicator of immune function.

When an individual's CD4 count falls below 200 cells per cubic millimeter of blood, it signifies a significant level of immune suppression, leading to an increased risk of opportunistic infections and certain cancers, which are characteristic of AIDS. This threshold helps clinicians determine the progression of HIV infection and the necessary interventions required to manage the patient's health effectively.

In the context of the other options, a CD4 count between 200 and 499 is indicative of a less advanced stage of HIV infection, while a count above 500 generally reflects a healthy immune system in those living with HIV. The option "Unknown" is not relevant in this clinical context, as established guidelines provide specific CD4 count cutoffs for diagnosing AIDS.