Thursday, July 8, 2010

HIV Antibody The Test

HIV Antibody The Test

  1. How is it used?
  2. When is it ordered?
  3. What does the test result mean?
  4. Is there anything else I should know?

How is it used?

HIV antibody testing is used to screen for and diagnose HIV infections. Early treatment of HIV infection and immune system monitoring can greatly improve long-term health. Also, knowing your HIV status may help you change behaviors that would put you and others at risk.

Antibodies to the HIV virus are often detected by a screening test called an ELISA. The ELISA test is repeated if positive. The ELISA method is very sensitive but requires another test, a Western Blot, to confirm the results because false positives can occur. These tests can be done on blood, urine or oral sample in a doctor’s office or a local clinic. There are several rapid tests available in which results are generated in about 20 minutes. However, these too must have confirmatory testing before a final diagnosis can be made.

There is also a home collection kit approved by the US Food and Drug Administration (FDA) that is available for HIV antibody testing. This allows you to take a sample of your blood from a finger at home and mail it to a testing center. You would then hear your results later over the phone, along with appropriate counseling. There are, however, no available tests that can be performed at home. (For more, see the article on Home Testing and the FDA webpage on HIV home tests.)


When is it ordered?

Several organizations, including the Centers for Disease Control (CDC), American College of Physicians (ACP), and HIV Medicine Association (HMA) recommend that anyone over the age of 13 be screened for HIV.

Antibody testing for HIV is especially important if you are in a high risk group or if you think you may have been exposed to HIV. Testing is recommended if:

  • You are sexually active (three or more sexual partners in the last 12 months).
  • You received a blood transfusion prior to 1985, or a sexual partner received a transfusion and later tested positive for HIV. For more information, see the CDC webpage How safe is the blood supply in the US?
  • You are uncertain about your sexual partner’s risk behaviors.
  • You are a male who has had sex with another male.
  • You have used street drugs by injection, especially when sharing needles and/or other equipment.
  • You have a sexually transmitted disease (STD).
  • You are a health care worker with direct exposure to blood on the job.
  • You are pregnant. (There are now treatments that can greatly reduce the risk that a pregnant woman who has HIV will give the virus to her baby.)
  • You are a woman who wants to make sure you are not infected with HIV before getting pregnant (see Pregnancy: Pre-conception, HIV).


What does the test result mean?

A healthy individual has no antibodies to HIV. However, a negative screening test means only that there is no evidence of disease at the time of the test. It is important for those who are at increased risk of HIV infection to have screening tests performed on a regular basis to check for possible exposure to the virus.

If you test positive for HIV antibodies on both the ELISA and the Western Blot tests, you are considered to be infected with HIV. HIV cannot be cured, but early diagnosis allows for treatment that can help to suppress levels of virus in your body (viral load) and slow progression of the disease.


Is there anything else I should know?

Antibody testing will not detect HIV immediately after exposure, during the window before the development of antibodies. If you are tested too soon, your result may be negative despite the fact that you are infected (false negative). In this case, you may be tested using a p24 antigen test that can detect actual viral protein in the blood 1 to 3-4 weeks after exposure or an HIV RNA test (viral load) that detects the presence of the virus, not the antibody response to it. Or you should have another HIV antibody test in 3–6 months from the time of a possible exposure to the virus.

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