Types of HIV tests
| Test type | What it detects | Window period |
|---|---|---|
| 4th generation Ag/Ab test (standard) | HIV p24 antigen + HIV-1/2 antibodies | 18–45 days |
| 3rd generation Ab-only test | HIV-1/2 antibodies only | 23–90 days |
| HIV RNA (viral load) test | HIV genetic material | 10–33 days (earliest detection) |
| Rapid/point-of-care test | HIV-1/2 antibodies | 23–90 days |
What is the window period?
Why timing matters for HIV testing
The window period is the time between HIV infection and when a test can reliably detect it. During this period, a person is infected and infectious but may test negative. Modern 4th generation tests (the standard in most clinics) detect both the p24 antigen (an early viral protein) and antibodies, shortening the window period to about 18–45 days. A negative result at 45 days is considered conclusive for 4th generation tests. For 3rd generation tests, the conclusive period is 90 days.
HIV test results
| Result | Meaning | Next step |
|---|---|---|
| Non-reactive (negative) | No HIV detected | Retest if within window period or ongoing risk |
| Reactive (preliminary positive) | Possible HIV infection | Confirmatory testing required |
| Confirmed positive | HIV infection present | Start HIV care and antiretroviral therapy (ART) |
PrEP and PEP
PrEP (pre-exposure prophylaxis) is a daily medication that prevents HIV in HIV-negative high-risk individuals — over 99% effective. PEP (post-exposure prophylaxis) is emergency medication started within 72 hours of a potential exposure — it must be started as soon as possible. Regular HIV testing is recommended for people on PrEP (every 3 months).
Questions to ask your doctor
- Which generation HIV test am I having?
- When was my potential exposure — am I still in the window period?
- Am I eligible for PrEP?
- If positive — what is my CD4 count and viral load?