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Antithyroid microsomal antibody

Antithyroid microsomal antibody is a test to measure antithyroid microsomal antibodies in the blood. Microsomes are found inside thyroid cells. The body produces antibodies to microsomes when there has been damage to thyroid cells.

Alternative Names

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

How the test is performed

A blood sample is needed. For information on how this may be done, see: Venipuncture

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.

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  affecting the thyroid.

Normal Values

A negative test is normal.

Normal value ranges may vary slightly among different laboratories. Talk to your doctor 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 to an increased risk of:

Anti-microsomal antibodies may be seen in your blood if you have other auto-immune conditions such as rheumatoid arthritis, systemic lupus erythematosus ,Sjogren syndrome, and auto-immune hemolytic anemia. However, this alone does not mean that the thyroid is abnormal. However, a positive result typically suggests that you are susceptible to thyroid disease in the future.

What the risks are

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)

References

Kim M, Ladenson P. Thyroid. In: Goldman L, Schafer AI, eds. Cecil Medicine. 24th ed. Philadelphia, PA: Saunders Elsevier; 2011:chap 233.

Salvatore D, Davies TF, Schlumberger MJ, Hay ID, Larsen PR. Thyroidphysiology and diagnostic evaluation of patients with thyroid disorders. In: Melmed S, Polonsky KS, Larsen PR, Kronenberg HM, Larsen PR, eds. Williams Textbook of Endocrinology. 12th ed. Philadelphia, Pa: Saunders Elsevier;2011:chap 11.

Updated: 6/26/2012

Shehzad Topiwala, MD, Chief Consultant Endocrinologist, Premier Medical Associates, The Villages, FL. Review provided by VeriMed Healthcare Network. Also reviewed by David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine, and David Zieve, MD, MHA, Medical Director, A.D.A.M. Health Solutions, Ebix, Inc.


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