Certified in Public Health (CPH) Practice Exam

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In the absence of HIV infection, the CD4+ T lymphocyte count of a healthy individual is approximately 2,000 cells/µl. How much does this count have to fall to as part of the diagnosis of AIDS?

1,000
500
200
10

The correct answer is: 200

A diagnosis of AIDS (Acquired Immunodeficiency Syndrome) is made when an individual's CD4+ T lymphocyte count falls below a critical threshold, indicating severe immunosuppression. The specific count that defines the progression from HIV infection to AIDS is typically recognized as 200 cells/µl or lower. This marked decline in CD4+ T cells signifies that the immune system is compromised, leading to increased vulnerability to opportunistic infections and certain cancers, which are hallmark indicators of AIDS. In a healthy individual, the normal range of CD4+ T lymphocytes is much higher, often around 1,000 to 1,600 cells/µl. Therefore, when the count drops to 200 cells/µl, it reflects a significant reduction in immune function, confirming that the individual has progressed to AIDS. Understanding this cut-off is crucial for public health and clinical settings, as it guides treatment decisions and the management of patients living with HIV.