What is a key indicator for diagnosing AIDS?

• A. Positive result on a rapid HIV test
• B. Presence of a chronic infection
• C. Serum CD4 count less than 200
• D. HIV antibodies detected in saliva

Answer: (C)

The presence of a serum CD4 count less than 200 is a crucial criterion for diagnosing AIDS, as it reflects the degree of immune system impairment caused by HIV infection. CD4 T cells play a vital role in the immune response, and a count below this threshold indicates significant immunosuppression. This condition makes individuals much more susceptible to opportunistic infections and certain cancers, which are key features of AIDS.

While a positive result on a rapid HIV test can confirm HIV infection, it does not indicate the progression to AIDS. The presence of a chronic infection may describe a clinical picture seen in AIDS but is not specific enough for diagnosis. Similarly, detecting HIV antibodies in saliva indicates exposure to the virus but does not provide the necessary information about immune status or progression to AIDS. Thus, the serum CD4 count is the definitive measure used in clinical guidelines to diagnose AIDS.