What are high thyroid peroxidase antibodies?

Written by mark bingaman
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The thyroid often suffers as the body turns on itself, sending the immune system to mistakenly attack this crucial gland. High thyroid peroxidase antibodies often signal that this battle is under way and help physicians formulate a defence.


Thyroid peroxidase (TPO) is an enzyme in the thyroid gland that plays a vital role in the production of thyroid hormone. So, what are high thyroid peroxidase antibodies? A thyroid peroxidase test determines the level of antibodies in the blood that are fighting against TPO and damaging the ability of this enzyme to do its job.

"The presence of thyroid peroxidase antibodies in your blood suggests that the cause of thyroid disease is due to an autoimmune disorder such as Hashimoto's disease or Graves' disease," according to Dr. Todd Nippoldt, an endocrinologist with the Mayo Clinic. "In autoimmune disorders, your immune system makes antibodies that mistakenly attack normal tissue." This causes inflammation and short-circuits the thyroid's ability to properly function.


Those who have been diagnosed with thyroid disease will typically undergo a thyroid peroxidase antibody test in order to determine the specific cause. It is meant to investigate why a goitre (an enlarged thyroid or a lump of cells, called a nodule) has developed. Physicians will usually order a TPO when other test results measuring the levels of T3 or T4 hormone or TSH (thyroid stimulating hormone) show irregularities.

Non-Thyroid Disorders

A test also may be ordered for those with non-thyroid related auto-immune conditions like lupus, rheumatoid arthritis, or pernicious anaemia, should those patients begin showing symptoms of possible thyroid issues. This often is the case for women with these disorders, or a known diagnosis of Hashimoto's or Graves' disease, who become pregnant. A TPO will be conducted both at the beginning and end of the pregnancy to determine whether the baby is at risk of developing thyroid disease.


High concentrations of thyroid peroxidase antibodies suggest the presence of Hashimoto's or Graves' Disease. However, some variables exist in the testing. "The sensitivity and specificity of thyroid antibody testing is improving but is still not as good as doctors would like it to be," says the American Association for Clinical Chemistry. "All of the thyroid antibody tests have changed over time. There are also many distinct methodologies and each has different reference (normal) ranges."

For this reason, it is important that you use the same laboratory, using the same methods, to test regularly to monitor your condition.

Hashimoto's Disease

Also known as Hashimoto's thyroiditis, this disease is a reaction of the immune system against the thyroid, causing inflammation and reduced function. "You may receive thyroid hormone replacement therapy (levothyroxine) if your body is not producing enough of the hormone," according to the University of Wisconsin's School of Medicine and Public Health.

Graves' Disease

Although both are the result of the immune system mistakenly attacking the thyroid, Graves' disease is the opposite of Hashimoto's disease in that it brings on hyperthyroidism (overactivity of the thyroid), causing it to produce excessive levels of the hormone thyroxine. The condition is usually treated with medication or radioactive iodine.

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