How do antibody tests work?
When a person is infected with HIV, their body responds by producing special proteins that fight infection, called antibodies. An HIV antibody test looks for these antibodies in blood, saliva or urine. If antibodies to HIV are detected, it means a person has been infected with HIV. There are only two exceptions to this rule:
- Babies born to HIV infected mothers retain their mother's antibodies for up to 18 months, which means they may test positive on an HIV antibody test, even if they are actually HIV negative. Normally babies who are born to HIV positive mothers receive a PCR test (see below) after birth.
- Some people who have taken part in HIV vaccine trials may have HIV antibodies even if they are not infected with the virus.
Most people develop detectable HIV antibodies within 6 to 12 weeks of infection.