Alternate Names: Western blot; ELISA/western blot - HIV
How 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.
The ELISA and western-blot are 2 different laboratory techniques used to detect the presence of antibodies.
How To Prepare: 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 It Feels: 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.
Risks:
- excessive bleeding
- fainting or feeling lightheaded
- hematoma (blood accumulating under the skin)
- infection (a slight risk any time the skin is broken)
- multiple punctures to locate veins
Normal Values: A negative test result is normal.
Abnormal Results: The ELISA is used as a screening test. A positive result does not necessarily mean that the subject has exposure to the HIV virus or HIV disease. The western-blot is used as a confirmatory test, and may be negative, positive, or indeterminate. A positive western blot is generally regarded as conclusive for an HIV infection. Negative tests 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 anti-HIV ELISA or western-blot test).
Note: Studies have shown that a recent flu shot can result in a false positive HIV ELISA. However, if this is the reason you tested positive 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.
Cost:
Special Considerations: This test may be repeated after a time, or other tests performed, if HIV disease is suspected and the results of the test are negative.
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.
