These tests are used to confirm the diagnosis of Lyme disease.

Blood is drawn from a vein on the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and an elastic band is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the band to 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 band 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.

For an 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.

For the screening test, a test called an ELISA is done as follows: the spirochete Borrelia burgdorferi, the organism that causes Lyme disease, is grown in culture and placed on a microscope slide. The slide is then incubated with a sample of your serum (the portion of blood that contains antibodies). A substance called an antiglobulin is placed on the slide. This antiglobulin has been treated so that it glows fluorescent in ultraviolet light. If human antibody to Lyme disease is present, it will attach to the fluorescent antiglobulin and be visible under the ultraviolet light.

Another test, called the Western blot, can truly confirm the presence of Lyme disease.

There is no special preparation for the test.

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.

The test is performed to help confirm the diagnosis of Lyme disease.

Nonreactive or a very low serum titer (antibody count) are normal.

Only a positive Western blot test can confirm the diagnosis of Lyme disease. A positive ELISA can help confirm the diagnosis, but isn't enough by itself because other infectious diseases and some types of inflammatory diseases such as rheumatoid arthritis can give the same results.

The risks associated with having blood drawn are:

• Excessive bleeding
• Fainting or feeling light-headed
• Hematoma (blood accumulating under the skin)
• Infection (a slight risk any time the skin is broken)
• Multiple punctures to locate veins

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.