Thyroid peroxidase (TPO) antibodies are abnormal molecules found in autoimmune diseases such as Hashimoto’s thyroiditis and Graves’ disease. Elevated levels are associated with thyroid problems and increased risk of reproductive issues. Asymptomatic people may also have detectable levels and are at risk of future thyroid problems. Doctors may check for TPO antibodies before prescribing certain medications.
When the body attacks certain parts of its own thyroid gland, evidence of this can be found in the presence of abnormal molecules called thyroid peroxidase (TPO) antibodies. Other terms for these substances are antithyroid microsomal antibodies or antiperoxidase antibodies. Elevated levels are most closely associated with Hashimoto’s thyroiditis but can also be seen with Graves’ disease. A certain percentage of asymptomatic people with no thyroid problems test positive for this antibody, and these people are at increased risk of developing thyroid abnormalities in the future.
In general, the presence of thyroid peroxidase antibodies in the blood is an abnormal finding. Antibodies are proteins produced by the immune system that help fight bacteria or other threats to the body’s health. Although the body normally only makes antibodies against foreign substances, in a certain class of diseases called autoimmune diseases, the body makes antibodies against elements of itself. With the production of TPO antibodies, the body produces a protein that attacks a molecule important to thyroid function, the enzyme thyroid peroxidase. This substance is essential for the creation of thyroglobulin, which is a protein that carries thyroid hormone through the blood to distant parts of the body.
A positive result for the presence of thyroid peroxidase antibodies is most often found in autoimmune thyroiditis, a condition also known as Hashimoto’s thyroiditis. Patients with this disease create antibodies that attack the thyroid gland. Eventually they experience a decrease in thyroid hormone production, a condition known as hypothyroidism. Many physicians consider finding positive TPO antibodies in a patient with hypothyroidism to be diagnostic of Hashimoto’s thyroiditis. The mainstay of treatment for this condition is providing the patient with a thyroid hormone supplement in pill form.
Having antibodies to thyroid peroxidase is also associated with a number of other conditions. Patients with Graves’ disease, an autoimmune thyroid disease that causes the thyroid gland to overproduce thyroid hormone, may have antibodies to thyroid peroxidase present in their blood. Some studies have suggested that women who produce this antibody are at increased risk of developing reproductive problems such as early pregnancy, miscarriages and infertility.
Some normal, asymptomatic people may have detectable levels of thyroid peroxidase antibodies. Up to 5 to 10 percent of the general population would have positive results on this lab test, if controlled. While many times these people don’t have any symptoms, they may be at risk of having problems with thyroid function in the future. Some doctors check for this antibody level before starting certain medications that could lead to hypothyroidism, including amiodarone and lithium, because they may choose not to use these medications in patients who are already at risk of developing problems with thyroid hormone production.
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