Which of the following is a diagnostic laboratory test for acquired immunodeficiency syndrome (AIDS)?

The presence of less than 200 CD4+ T cells is a critical indicator for diagnosing acquired immunodeficiency syndrome (AIDS) as defined by the Centers for Disease Control and Prevention (CDC). CD4+ T cells are a type of white blood cell that plays a significant role in the immune system; they help the body fight off infections. A count below 200 cells per cubic millimeter is indicative of severe immune system compromise, which aligns with the diagnosis of AIDS when a patient is infected with the human immunodeficiency virus (HIV).

Low CD4+ T cell counts signify that the immune system is severely weakened, making the individual more susceptible to opportunistic infections and certain cancers, which are characteristic of AIDS. Therefore, a CD4+ T cell count below 200 is not only a lab test but a defining characteristic of the progression from HIV infection to AIDS, reflecting the urgency for medical intervention and treatment.

While other options such as the presence of HIV antibodies, high viral load, and the presence of opportunistic infections provide valuable information about the HIV infection and disease progression, they do not alone confirm a diagnosis of AIDS. The CD4+ T cell count remains a definitive laboratory measure in this context.