What it measures
Antibodies to HIV-1 and HIV-2 together with the p24 antigen, a protein from the virus itself. Because p24 appears before antibodies, this fourth-generation test picks up an infection sooner than an antibody-only test. It is the standard HIV test in UK labs.
Why people test it
- A routine check after a new partner, or as part of a sexual health screen.
- Checking after possible exposure, such as condomless sex, shared needles or a needlestick injury.
- Routine screening in pregnancy, before some medical procedures or for some jobs.
Typical range
There is no numeric range. The result is reported as reactive or non-reactive (sometimes positive or negative), and a reactive result is confirmed with further tests before a diagnosis is made. The report shows how that lab reports it.
Finger-prick or vein?
A finger-prick sample is usually fine for this test, and several providers offer a home kit. Others take blood from a vein, at a clinic or with a visiting nurse.
The 2020 UK HIV testing guidelines (BHIVA, BASHH and BIA) give a window period of 45 days for a fourth-generation lab test: the time it can take for an infection to show.