Broadly speaking, AIDS is diagnosed when cell-mediated immunity is lost, meaning the immune system can no longer successfully combat HIV or other infections. There are three diagnostic criteria, as defined by the Centers for Disease Control and Prevention, for an AIDS diagnosis.
T-Cell Count
HIV attacks cells of the immune system (lymphocytes) called CD4+. A count of lower than 200 per cubic milliliter of blood is the primary diagnostic criterion for AIDS.
T-Cell Percentage
Taken as a percentage of lymphocytes, a CD4+ percentage of less than 14 is a diagnostic criterion for AIDS.
Opportunistic Infections
Before the cause of AIDS was known, the presence of opportunistic infections, which occur only in people with severely compromised immune systems, was the only way to diagnose AIDS. The presence of these conditions, such as thrush, cytomegalovirus, Kaposi's sarcoma, pneumocystis pneumonia and many others, remains a diagnostic criterion for AIDS.
Significance
No matter which criterion is used, a diagnosis of AIDS means that the immune system, which had previously been able to control HIV alongside other infections, is no longer able to do so (cell-mediated immunity is lost). Too many CD4+ have been infected by HIV for the immune system to continue to function normally.
Treatment
Treatment with antiretroviral drugs often delays the onset of AIDS. Almost all untreated HIV cases will progress to an AIDS diagnosis.
Tags: immune system, criterion AIDS, diagnostic criterion, diagnostic criterion AIDS, AIDS diagnosis, cell-mediated immunity, cell-mediated immunity lost
