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Antithyroid microsomal antibody

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.

Why the Test is Performed

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

The test is also used to find out if an immune or autoimmune disorder is damaging the thyroid.

Normal Results

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:

High levels of these antibodies have also been linked with an increased risk of:

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.

Antithyroid microsomal antibodies may be seen in your blood if you have other autoimmune conditions, including:


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
  • Hematoma (blood buildup under the skin)
  • Infection (a slight risk any time the skin is broken)

Alternative Names

Thyroid antimicrosomal antibody; Antimicrosomal antibody; Microsomal antibody; Thyroid peroxidase antibody; TPOAb



Salvatore D, Davies TF, Schlumberger MJ, et al. Thyroid physiology and diagnostic evaluation of patients with thyroid disorders. In: Melmed S, Polonsky KS, Larsen PR, Kronenberg HM, Larsen PR, et al, eds. Williams Textbook of Endocrinology. 12th ed. Philadelphia, PA: Elsevier; 2016:chap 11.

Weiss RE, Refetoff S. Thyroid function testing. In: Jameson JL, De Groot LJ, eds. Endocrinology: Adult and Pediatric. 7th ed. Philadelphia, PA: Elsevier Saunders; 2016:chap 78.

Review Date 2/3/2016

Updated by: Brent Wisse, MD, Associate Professor of Medicine, Division of Metabolism, Endocrinology & Nutrition, University of Washington School of Medicine, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.