HIV Combo (Antigen And Antibody) Test
What is HIV Combo (Antigen And Antibody) Test?
HIV 1 And 2 Antibody test is done to confirm the presence of HIV-1 and HIV-2 antibodies in the blood. Human immunodeficiency virus (HIV) is a virus that can be transmitted through unsafe sexual contact with an infected person or through body fluids like blood, semen and breast milk.
Most people produce detectable levels of antibodies 3 to 12 weeks after exposure. Thus, if someone is tested too soon for HIV infection, the result may be negative even though the person is infected. This test is ordered for people exposed to HIV, such as those who indulge in unsafe sex, share needles or have had blood transfusions, and those with any sexually transmitted diseases.
Why is HIV Combo (Antigen And Antibody) Test done?
To screen for and diagnose HIV infection
If you are pregnant or planning to get pregnant
If you are diagnosed with Hepatitis B, C, Tuberculosis, or any other sexually transmitted disease
Annual screening is advised for those who are at high risk for HIV infection like having an HIV positive sex partner, multiple sexual partners, homosexual people, and sharing needles
To differentiate HIV-1 and HIV-2 antibodies in specimens of serum that show reactive results with third and fourth generation HIV serologic assays
What does HIV Combo (Antigen And Antibody) Test Measure?
Acquired Immunodeficiency Syndrome (AIDS) is caused by the Human Immunodeficiency Virus (HIV). HIV Virus is of two types: HIV-1 and HIV-2. HIV-1 is found in AIDS patients, AIDS-related complex patients, and those persons who are at high risk of getting affected by AIDS. HIV virus can be transmitted by sexual contact, exposure to blood or blood products of AIDS-infected patients, or transfer of infection from AIDS-infected mother to the fetus. Most of the cases of HIV-2 infected patients are seen in West Africa, and it is detected in patients who had sexual contact with people of that geographic region. These viruses have the same morphology, overall genomic structure, and ability to cause infection.
When the patient gets infected with the virus, the virus attacks the immune system called CD4 and combines with antibodies to use them for making a large number of copies inside the body of the patient by replication. During the first few weeks of infection, the amount of virus present and the level of p24 antigen in the blood becomes very high. After another 2-8 weeks, these increased levels start to fall as the body of the infected patient starts producing antibodies against the antigen of the virus. At this time, the HIV virus antibody can be detected in the patient’s blood via tests. The tests should be performed at this brief time because after some time both the levels of antigen and antibody in the blood falls. This will make the detection of virus infection difficult as the initial infection may have been resolved and you may not get a positive result against the infection.
The HIV antibody tests do not detect an HIV infection soon after exposure, before the development of antibodies. Most people produce detectable levels of antibody 3 to 12 weeks after exposure. If someone is screened with an HIV antibody test too soon, the result may be negative despite the fact that the person is infected. For those who are at increased risk of HIV infection, it is important to get this screening test done frequently to check for possible exposure to the virus.
This test is done by ELISA method which is also known as EIA for Enzyme Immunoassay. This test is done to analyze certain proteins which are produced by the body in response to HIV infection.
The blood sample is added to a cassette which contains the HIV antigen. If the patient’s blood contains HIV antibodies, they will bind with the antigen and there will be changes in the content of the cassette.
Interpreting HIV Combo (Antigen And Antibody) Test results
- A negative HIV antibody test usually indicates that a person does not have HIV infection. However, it only means that there is no evidence of disease at the time of the test.
- If someone tests positive on both the initial screening and supplemental testing, it is considered as a definite case of infection with HIV.