Microsomes are found inside thyroid cells. The body produces antibodies to microsomes when there has been damage to thyroid cells. The antithyroid microsomal antibody test measures these antibodies in the blood.
How the Test is Performed
A blood sample is needed.
How the Test will Feel
When the needle is inserted to draw blood, some people feel moderate pain. Others feel only a prick or stinging. Afterward, there may be some throbbing or a slight bruise. This soon goes away.
A negative test means the result is normal.
Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or may test different specimens. Talk to your health care provider about the meaning of your specific test results.
What Abnormal Results Mean
A positive test may be due to:
- Granulomatous thyroiditis (an immune reaction of the thyroid gland that often follows an upper respiratory infection)
- Hashimoto thyroiditis (a reaction of the immune system against the thyroid gland)
High levels of these antibodies have also been linked with an increased risk of:
- Preeclampsia (high blood pressure and protein in the urine after the 20th week of pregnancy)
- Premature birth
- In vitro fertilization failure
Important: A positive result does not always mean that you have a thyroid condition or that you need treatment for your thyroid. A positive result may mean that you have a higher chance of developing thyroid disease in the future. This is often associated with a family history of thyroid disease.
Antithyroid microsomal antibodies may be seen in your blood if you have other autoimmune conditions, including:
There is little risk involved with having your blood taken. Veins and arteries vary in size from one person 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 lightheaded
- Multiple punctures to locate veins
- Hematoma (blood buildup under the skin)
- Infection (a slight risk any time the skin is broken)
Thyroid antimicrosomal antibody; Antimicrosomal antibody; Microsomal antibody; Antithyroid microsomal antibody; TPOAb; Anti-TPO antibody
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Review Date 1/26/2020
Updated by: Brent Wisse, MD, board certified in Metabolism/Endocrinology, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.