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Alternative Names Return to top
HIV testingDefinition Return to top
HIV ELISA/Western blot is a set of blood tests used to diagnose chronic infection with human immunodeficiency virus (HIV).
How the Test is Performed Return to top
Blood is typically drawn from a vein, usually from the inside of the elbow or the back of the hand. The site is cleaned with germ-killing medicine (antiseptic). The health care provider wraps an elastic band around the upper arm to apply pressure to the area and make the vein swell with blood.
Next, the health care provider gently inserts a needle into the vein. The blood collects into an airtight vial or tube attached to the needle. The elastic band is removed from your arm. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.
In infants or young children, a sharp tool called a lancet may be used to puncture the skin and make it bleed. The blood collects into a small glass tube called a pipette, or onto a slide or test strip. A bandage may be placed over the area if there is any bleeding.
How to Prepare for the Test Return to top
No preparation is necessary. HIV testing requires written consent in most U.S. states.
How the Test Will Feel Return to top
When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.
Why the Test is Performed Return to top
Testing for HIV infection is done for many reasons, including:
Normal Results Return to top
A negative test result is normal. However, early HIV infection (termed acute HIV infection or primary HIV infection) often results in a negative test.
What Abnormal Results Mean Return to top
A positive result on the ELISA screening test does not necessarily mean that the person has HIV infection. There are certain conditions that may lead to a false positive result, such as Lyme disease, syphilis, and lupus.
A positive ELISA test is always followed by a Western blot test. A positive Western blot can usually confirm an HIV infection.
Negative tests do not rule out HIV infection. There is a period of time (called the "window period") between HIV infection and the appearance of anti-HIV antibodies that can be measured.
If a person might have acute or primary HIV infection, and is in the "window period," a negative HIV ELISA and Western blot will not rule out HIV infection. More tests for HIV will need to be done.
Risks Return to top
Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.
Other risks associated with having blood drawn are slight but may include:
Considerations Return to top
People who are at high risk (men who have sex with men, injection drug users, commercial sex workers) should be regularly tested for HIV.
If the health care provider suspects early (acute or primary) HIV infection, other tests (such as HIV viral load) will be needed to confirm this diagnosis, because the HIV ELISA/Western blot will often be negative during this window period.
Update Date: 1/22/2008 Updated by: Kenneth M. Wener, MD, Department of Infectious Diseases, Lahey Clinic, Burlington, MA. Review provided by VeriMed Healthcare Network.
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Page last updated: 25 September 2008 |