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.

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

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

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 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.

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.

A positive test may be due to:

• Granulomatous thyroiditis
• Hashimoto's thyroiditis

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

• Miscarriage
• Preeclampsia
• Premature birth
• In vitro fertilization failure

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.

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)

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.