Antithyroglobulin antibody is a test to measure antibodies to a protein called thyroglobulin, which is found in thyroid cells.

Blood is 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.

You may be told not to eat or drink anything for several hours before the test (usually overnight). Your doctor may monitor or tell you to stop taking medications that may affect test results until after 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.

This test helps detect possible thyroid problems. Antithyroglobulin antibodies can lead to the destruction of the thyroid gland. Such antibodies are more likely to appear after thyroid gland swelling (inflammation) or injury.

Thyroglobulin antibody is also measured whenever the thyroglobulin level is measured.

A negative test is normal. A negative test means no antibodies to thyroglobulin are found in your blood.

Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.

A positive test means antithyroglobulin antibodies are found in your blood. This may be due to:

• Graves disease
• Hashimoto's thyroiditis
• Hypothyroidism
• Myxedema
• Systemic lupus erythematosus (SLE)
• Thyroid cancer
• Thyrotoxicosis
• Type 1 diabetes

Pregnant women and relatives of those with autoimmune thyroiditis may also test positive for these antibodies.

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:

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

Ladenson P, Kim M. Thyroid. In: Goldman L and Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders; 2007:chap 244.