The Test Sample
What is being tested?
Human immunodeficiency virus (HIV) is the cause of AIDS (acquired immunodeficiency syndrome). This test detects antibodies produced in response to an HIV infection. The antibodies may be detected in blood or other body fluids, such as oral fluid or urine.
An HIV infection may initially cause no symptoms or cause flu-like symptoms that resolve after a week or two. This is followed by a simmering infection that may cause few symptoms for a decade or more. If the infection is not treated, eventually symptoms of AIDS emerge and begin to progressively worsen. Over time, HIV destroys the immune system and leaves a person's body vulnerable to debilitating infections. There are two types of HIV, 1 and 2. HIV-1 is the most common type found in the United States, while HIV-2 has a higher prevalence in parts of Africa.
When HIV enters the body, such as through exposure to the blood or body fluids of an infected individual or contaminated needle, the immune system responds by producing antibodies directed against the virus. These antibodies can be detected with screening tests about 2 to 8 weeks after exposure to the virus. If exposure to the virus is more recent, then antibody levels may be too low to detect and repeat testing at a later time may be required.
A few different options are available for HIV antibody screening. All HIV tests used in the U.S. detect HIV-1, and some types have been developed that can also detect HIV-2. Some versions can detect both HIV antibody and an HIV marker called the p24 antigen. Levels of p24 antigen are typically high early in the course of infection. An antibody/antigen combination test may be performed to increase the likelihood that HIV infection is detected sooner after exposure occurs.
Depending on the test, antibody screening may be performed on a sample of blood or oral fluid. The sample may be collected at a doctor's office or local clinic and sent to a laboratory for testing. Rapid antibody tests may be available in these settings and can provide results in about 20 minutes. Some tests are designed so that a sample can be collected at home and then sent to a laboratory. The Food and Drug Administration (FDA) approved in July 2012 a test for use at home. Though the test has limitations, the FDA felt the potential benefit of increasing the number of people tested for HIV outweighs the drawbacks of possible errors when the test is performed at home. (For more on this, see the article Home Testing: Avoiding Errors.)
Regardless of the type of antibody screening test used, a positive result requires follow up with supplemental testing to establish a diagnosis of HIV.
Detecting and diagnosing HIV early in the course of infection is important because:
- It allows for early treatment that slows progression to AIDS.
- An individual can learn of their status and modify behavior so as to prevent the spread of disease by not exposing others to their blood or body fluids.
- A pregnant woman can undergo treatment that would help prevent her spreading the disease to her child.
How is the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein in the arm. There also are tests available that can be performed on oral samples. An oral sample is obtained by using a special small, spatula-like device with a flat pad on the end. The flat pad is placed above the teeth against the outer gum and is swabbed completely once around the outer part of 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.