HIV ELISA/Western blot
Alternative names:
ELISA/western blot - HIV; western blot
Overview:
The HIV antibody test screens for exposure to the human immunodeficiency virus (HIV). A positive test suggests that the individual has been infected with HIV.
Preparation:
No physical preparation is necessary. Many institutions will perform counseling prior to performing the HIV antibody test. A special written consent form is obtained before performing the HIV antibody test in most states, but a few states do not require any formal written consent.
Infants and children:
The physical and psychological preparation you can provide for this or any test or procedure depends on your child's age, interests, previous experience, and level of trust. For specific information regarding how you can prepare your child, see the following topics as they correspond to your child's age:
How the test is performed:
Adult or child:
Blood is drawn from a vein (venipuncture), usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and a tourniquet (an elastic band) or blood pressure cuff is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the tourniquet to distend (fill with blood). A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. During the procedure, the tourniquet is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.
Infant or young child:
The area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. Cotton or a bandage may be applied to the puncture site if there is any continued bleeding.
Blood in the tube or syringe is transported to the laboratory to perform the HIV antibody test (ELISA and Western Blot). The ELISA and western-blot are 2 different laboratory techniques used to detect the presence of antibodies to HIV, which is what the body produces to try and fight off the HIV infection, if it's present. These results may take up to one week to be generated, and are not typically given over the telephone (regardless of whether the result is positive or negative). There is also post-test counseling available in most clinics when you get the result of your test.
Duration of test-
The test itself will last only five to ten minutes, depending on the time it takes to draw the blood. The results may take one to two weeks to be processed and returned to your physician's office.
Results-
The HIV antibody test will give three possible results: (1) Negative, (2) Positive, or (3) Indeterminate. The blood is initially screened for the antibodies specific for HIV with a laboratory test called an ELISA. A negative test result is normal. A positive ELISA result does not necessarily mean that the subject has exposure to the HIV virus or HIV disease. With all positive ELISA tests, a Western-blot is used as a confirmatory test, and may be negative, positive, or indeterminate. A positive Western blot generally means that the person has an HIV infection. Indeterminate test results mean that the test results did not show clearly either positive or negative results. Since the test was inconclusive, another HIV antibody test needs to be taken within 1-2 months time. Negative Western blot tests mean that no antibodies to HIV were detected. However, they do not necessarily rule out HIV infection, because there is a time interval between HIV infection and the appearance of measurable anti-HIV antibodies (the so-called "window period"). An infected individual may transmit HIV during the window period (even with a negative HIV ELISA or Western-blot test). Thus, the HIV antibody test needs to be done three months after a possible exposure to HIV (i.e. via sex, needle-sharing) and then repeated at six months. A negative result at six months suggests with 99% assurance that the individual tested is not infected with HIV.
Note: Studies have shown that a recent flu shot can result in a false positive HIV ELISA. However, if you tested positive on the HIV ELISA because you recently had a flu shot, the Western-blot test will confirm that you are HIV negative. After about 3 months, the HIV ELISA will convert back to a negative result. Inform your health care provider if you are considering having this test performed and have had a flu shot within the past 3 months.
How to prepare for the test:
No physical preparation is necessary. Many institutions will perform counseling prior to performing this test. In some cases a special written consent form is obtained.
Infants and children:
The physical and psychological preparation you can provide for this or any test or procedure depends on your child's age, interests, previous experience, and level of trust. For specific information regarding how you can prepare your child, see the following topics as they correspond to your child's age:
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.
Update Date: 04/01/00
Luis A. Diaz, Jr. M.D., Johns Hopkins Medical Institute, VeriMed Health Network
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