Antithyroid microsomal antibody

Definition

This is a test to measure antithyroid microsomal antibodies in the blood. Microsomes are small cell particles. The body produces microsomal antibodies when these small cell particles escape from damaged thyroid cells.

A blood test can be done to detect and measure the amount of these antibodies in the blood.

Alternative Names

Why the Test is Performed

This test is done to confirm the cause of thyroid problems, including Hashimoto's thyroiditis .

The test may also be used to diagnose other autoimmune disorders.

How the Test is Performed

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.

How to Prepare for the Test

You may be told not to eat or drink for 6 to 8 hours before the test (usually overnight). Medications that affect the test results will be monitored or discontinued during the test.

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.

Risks

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)

Normal Results

A negative test is normal.

What Abnormal Results Mean

A positive test may be due to:

• Autoimmune hemolytic anemia
• Granulomatous thyroiditis
• Hashimoto's thyroiditis
• Nontoxic nodular goiter
• Rheumatoid arthritis
• Sjogren syndrome
• Systemic lupus erythematosus
• Thyroid cancer

Additional conditions under which the test may be performed:

• Autoimmune hepatitis

Increased levels of these antibodies have also been linked to an increased risk of miscarriage, preeclampsia, premature birth, and in vitro fertilization failure.