Overview
The HIV fourth-generation test detects both p24 antigen and HIV antibodies, allowing earlier detection than antibody-only tests in many situations.
What it detects
HIV-1 p24 antigen and HIV-1/HIV-2 antibodies.
Sample type
Blood sample.
When it may be appropriate
Routine screening and diagnostic evaluation after possible exposure.
Window period considerations
Often detects infection earlier than antibody-only tests, but very recent exposure may still be too early.
Test limitations
A reactive result still needs confirmation. False positives and false negatives can occur.
Interpretation basics
Nonreactive usually means no detectable infection at that time; reactive requires confirmatory testing.
Follow-up recommendations
Confirm reactive results and consider repeat testing if exposure was very recent.
Key points
- Earlier detection than antibody-only tests
- Blood-based screening
- Still requires confirmation
- Timing matters
When to seek care
- Routine HIV screening
- Recent exposure beyond antibody window
- Positive screen follow-up