June 27 is the National HIV Testing Day. The U.S. Centers for Disease Control and Prevention (CDC) recommends that people in the high-risk groups for HIV should get tested for HIV once a year. Here is some information on the different types of HIV tests that are used for detecting the presence of the human immunodeficiency virus.
Human immunodeficiency virus (HIV) is a virus that causes acquired immunodeficiency syndrome (AIDS). AIDS is a deadly disease that is well-known for its adverse effect on the body’s immune system. One can be exposed to this virus if one has unprotected sex with an infected person. This virus could also get transmitted through transfusion of infected blood. The use of syringes or needles contaminated with this virus is another contributory factor. This virus can also get transmitted from a pregnant woman to her unborn child. Once this virus enters the body, it targets the immune system, thereby making one highly susceptible to infections and diseases. Those who feel that they may have been exposed to this virus must get themselves tested for HIV.
When the specialized cells and structures of the immune system detect this virus, they respond by producing HIV antibodies. The development of detectable antibodies that are specific to the antigen is medically referred to as seroconversion. An infected person would test positive for HIV only after the antibodies can be detected in the blood, oral fluid or the urine sample. The time between the onset of the infection and the development of antibodies is referred to as the window period. The outcome of the screening test is therefore dependent on when the test is performed. The outcome could be false negative if the test is performed during the window period. Thus, people who are in the high-risk group must have these tests performed on a regular basis. These days, various types of HIV tests are being used for diagnosing this serious disease.
Diagnostic Tests for HIV
The detection of HIV antibodies is one of the most commonly used methods for diagnosing this disease. While blood samples are mostly used to test for HIV, urine or oral fluid samples could also be used for the same purpose. While HIV home test kits are also available, all of these kits are not approved by the FDA. Home Access HIV-1 Test System by Home Access Health Corporation is a home test kit that is approved by the FDA. This kit allows the user to collect the blood sample at home. The blood sample can then be sent to the laboratory for testing. Here’s some information on the screening tests.
More often than not, individuals infected with HIV, develop antibodies within three to four months. However, the process of seroconversion may last longer for some people. Antibody tests should therefore be conducted at regular intervals.
- Enzyme immunoassay (EIA) or Enzyme-Linked Immunosorbent Assay (ELISA) are plate-based assays that are employed for detecting antibodies. ELISA is a sensitive HIV screening test that may use blood, urine or oral fluid samples. In this test, HIV antigen is coated on the 96-well microtiter plate. The patient’s serum is then applied over the surface of the plate. If the serum contains antibodies to HIV, these will bind to the antigen. The next step involves washing or rinsing the plate to get rid of particles other than the antibodies and the antigens. A secondary antibody which is linked to an enzyme is then added to the plate. When the substrate (a substance/reactant acted upon by an enzyme) is added, a reaction takes place between the substrate and enzyme. A change in the color would be observed if the serum contains the virus. The immunoassay has evolved over the years. While the first generation ELISA utilized viral lysate antigen for the detection of IgG antibody, the second generation test is based on recombinant antigens. The third generation ELISA detects IgM as well as IgG antibodies. The fourth generation is used for the detection of the HIV antibody and the antigen.
- Though the ELISA test is considered to be quite reliable, test results would be generated in a couple of weeks. Rapid/Point of Care Tests tests are also available. The test results for rapid tests are available within 20 minutes. Either blood or an oral fluid sample may be used for these qualitative immunoassays. OraQuick Advanced Rapid HIV-1/2 Antibody Test, Uni-Gold, Reveal G2 HIV-1 Antibody Test and Multispot HIV-1/2 are some of the tests that fall under this category.
- Confirmation tests are performed if one tests positive for HIV antibodies in ELISA or if the outcome of the Rapid HIV test is preliminary positive. Western Blot test and Indirect Fluorescent Antibody (IFA) test are HIV antibody confirmation tests. The Western Blot test is commonly performed to confirm the results of the ELISA and rapid HIV tests.
p24 Antigen Test
An antigen is a substance that reacts with an antibody and triggers an immune system response. The p24 protein is a core protein of the human immunodeficiency virus. Though antibody tests are more commonly used for the diagnosis of this infection, doctors may sometimes order a p24 antigen test. While antibody test results can provide accurate results only after the seroconversion process is complete, p24 antigen test can be conducted in the first few weeks after one may have been infected. The levels of p24 antigen increase in the couple of weeks after one has been exposed to this virus, and only during this time, the patient’s serum can be tested for checking the levels of p24 antigen. This test involves mixing monoclonal antibodies that are specific to this protein to the blood sample. If p24 protein in present in the sample, it will bind to the antibody. Adding an enzyme-linked antibody to the monoclonal antibodies would bring about a color change. Due to its low sensitivity, this antigen test is not considered to be very effective.
PCR stands for Polymerase Chain Reaction test. PCR test, which is also known as viral load test, is used for measuring the amount of HIV in the blood sample. This test is also referred to as HIV NAAT. Nucleic acid amplification tests (NAAT) are considered to be more effective when it comes to diagnosing sexually-transmitted diseases. This is a fourth generation test. Unlike the aforementioned tests that are used for testing for antigens or antibodies, this test is used for detecting the genetic material of the human immunodeficiency virus. DNA/RNA amplification tests or qualitative PCR test may be used for testing infants born to women infected with HIV.
AIDS is a life-threatening disease. Since it makes one susceptible to recurring infections, it has an adverse impact on one’s quality of life. Thus, one must take all possible precautionary measures to prevent this disease. People who feel that they may have been exposed to HIV must get themselves tested. Those who test positive, must go for regular checkups and comply with the guidelines given by the doctors.