Definition of ELISA/Western blot tests for HIV:

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:

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:

No preparation is necessary. HIV testing requires written consent in most U.S. states.

How the test will feel:

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:

Testing for HIV infection is done for many reasons, including:

• Screening people who want to be tested
• Screening people in high-risk groups (men who have sex with men, injection drug users, and commercial sex workers)
• Screening people with certain conditions and infections (such as Kaposi's sarcoma, Pneumocystis pneumonia)
• Screening pregnant women to help prevent them from passing the virus to the baby