The Test Sample
What is being tested?
Human immunodeficiency virus (HIV) infects the cells of a person’s immune system and is the cause of AIDS (acquired immunodeficiency syndrome).
When a person becomes infected with HIV, through exposure to the blood or body fluids of an infected individual, the virus begins to reproduce very rapidly. So, during the first few weeks of infection, the amount of virus (viral load) in the blood can be quite high.
The immune system responds by producing antibodies directed against the virus and these begin to be detected in the blood around 3-4 weeks after exposure to the virus. As the level of HIV antibody increases, the viral load in the blood decreases.
This early HIV infection may cause no symptoms or sometimes a flu-like or glandular fever-type illness. The only way to determine whether a person has been infected is through HIV testing. Modern HIV screening tests detect HIV antigens (parts of the virus itself, usually a protein called the p24 antigen) and/or antibodies produced in response to an HIV infection.
Two main test types are available for HIV screening:
- Combination HIV antibody and HIV antigen test— this is the recommended screening test for HIV and is available only as a blood test. By detecting both antibody and antigen, the combination test increases the likelihood that an infection is detected soon after exposure. These tests can detect HIV infections in most people by 2-6 weeks after exposure.
- HIV antibody testing— This test takes a little longer to become positive after an exposure but can be carried out on blood or oral fluid. HIV antibody tests can detect infections in most people 3-12 weeks after exposure.
How is the sample collected for testing?
Blood is taken through a needle placed in a vein in your arm or sometimes by finger prick. Saliva is collected using a spatula with an absorbent pad on its tip which is swept around between the cheeks and the upper and lower gums.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.