Quick Answer
AIDS is diagnosed by testing for HIV and, if positive, checking for a severely weakened immune system or certain opportunistic infections. HIV is the virus; AIDS is the advanced stage of untreated infection. Modern treatment can keep HIV undetectable, which prevents progression to AIDS.
- HIV tests detect antibodies, antigens, or viral RNA, not AIDS itself.
- A CD4 count below 200 cells/mm3 indicates AIDS, per CDC criteria.
- An AIDS-defining illness, like Pneumocystis pneumonia, also confirms the diagnosis.
- Window periods vary by test type, from 10 to 90 days after exposure.
- A negative test after the window period is conclusive for HIV.
- Undetectable viral load means HIV is not transmissible, known as U=U.
The Short Version, Structured
Most people ask how AIDS is diagnosed, but the answer starts with HIV. AIDS is not a separate virus - it is the late stage of an untreated HIV infection. The diagnosis happens in two steps: first, confirm HIV is present; second, measure how much damage the virus has done to the immune system. This distinction matters because modern HIV treatment can stop the virus from replicating, keeping the immune system intact and preventing AIDS from ever developing. Understanding the testing process - what each test looks for, when to take it, and what the results mean - helps you act early and accurately.
Related Questions
Sources & Further Reading
- CDC — Sexually Transmitted Infections
- CDC STI Treatment Guidelines
- WHO — Sexually transmitted infections fact sheet
- MedlinePlus — Sexually Transmitted Diseases
Figures reflect CDC surveillance and WHO estimates; they are population statistics, not personal risk predictions.