What is a thyroid peroxidase antibody test? Does it diagnose thyroid disease?
Answer From Todd B. Nippoldt, M.D.
Thyroid peroxidase (TPO) is an enzyme normally found in the thyroid gland. TPO plays an important role in the production of thyroid hormones. A TPO test detects antibodies against TPO in the blood. If you've been diagnosed with thyroid disease, your doctor may suggest a TPO antibody test and other thyroid tests to help find the cause.
The presence of TPO antibodies in your blood suggests that the cause of thyroid disease is an autoimmune disorder, such as Hashimoto's disease or Graves' disease. In autoimmune disorders, your immune system makes antibodies that mistakenly attack normal tissue. Antibodies that attack the thyroid gland cause swelling, rarely tenderness and reduced function of the thyroid.
Your doctor may also order a TPO antibody test if you are pregnant and have an autoimmune disease that involves the thyroid, such as Hashimoto's disease or Graves' disease.
Some people with TPO antibodies may not have thyroid disease. But the presence of TPO antibodies may increase the risk of future thyroid disorders.
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July 16, 2022
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If your doctor has told you that you have elevated thyroid antibodies, but at the same time you have a normal thyroid stimulating hormone (TSH) level, what does that specifically mean as far as your thyroid condition?
What Are Antibodies?
Antibodies are proteins produced by your body that respond to or attempt to destroy antigens, substances such as viruses and bacteria that the body identifies as foreign.
In some cases, your body mistakenly identifies your own glands, tissues, and organs as foreign. This type of reaction is a characteristic of autoimmune disease, and these antibodies are called autoimmune antibodies.
Type of Antibodies
An important first step is to determine which type of antibodies are elevated. If you have elevated thyroid peroxidase (TPO) antibodies, that may point to the autoimmune thyroid disease known as Hashimoto’s thyroiditis. If you have elevated thyroid stimulating immunoglobulins (TSI), you may have autoimmune Graves’ disease.
Elevated Thyroid Peroxidase (TPO) Antibodies
If you have elevated TPO antibodies, even if your TSH level is normal, you most likely have Hashimoto's thyroiditis, an autoimmune disorder. In Hashimoto’s thyroiditis, the TPO antibodies attack your thyroid gland.
Over time, the TPO antibodies cause inflammation and eventually can destroy all or part of your thyroid gland.
Elevated Thyroid Stimulating Immunoglobulins (TSI)?
If you have elevated TSI antibodies, even if your TSH level is normal, you most likely have Graves’ disease, an autoimmune condition. In Graves’ disease, the TSI antibodies cause your thyroid gland to make too much thyroid hormone. As TSI antibodies cause overproduction of thyroid hormone, a TSH in the reference range drops, and you can become hyperthyroid fairly quickly.
What should you do?
If you have thyroid symptoms, but your TSH test result falls within the reference range, an important next step is to request that your doctor order thyroid antibody tests. If your symptoms suggest hypothyroidism—fatigue, weight gain, depression, hair loss—you should request a TPO antibody test. If your symptoms suggest hyperthyroidism—anxiety, insomnia, weight loss, diarrhea, elevated heart rate/blood pressure—you should request a TSI antibody test.
The Controversy Over Treating Thyroid Antibodies
As noted, many conventional physicians and endocrinologists believe that when your TSH is within the reference range and you are euthyroid, but you have elevated thyroid antibodies, your condition does not require treatment.
This is controversial, however, as research shows that the presence of thyroid antibodies alone can cause symptoms of hypothyroidism or hyperthyroidism.
With elevated TSI, there is usually a short period between the onset of elevated antibodies, and a TSH level that reflects hyperthyroidism. If you are experiencing acute symptoms of hyperthyroidism—such as elevated blood pressure or heart rate, or substantial weight loss—your doctor is likely to start treatment.
TPO antibodies can be elevated for longer periods before the TSH level shows hypothyroidism, so there are two different approaches your doctor may take toward treating Hashimoto’s thyroiditis.
Some doctors recommend a “wait and see,” approach, monitoring your TSH over time, and starting treatment only when your TSH goes above the reference range, typically a level above 4.0 to 5.0.
If you have hypothyroidism symptoms, some endocrinologists, as well as holistic and integrative physicians, will prescribe a trial of thyroid hormone replacement medication, even when your TSH is within the reference range.
While it remains a controversy, if you have elevated TPO antibodies and a normal TSH level, there is evidence that thyroid hormone replacement treatment may have benefits for you, including:
You may experience full or partial relief of your hypothyroidism symptoms
Your antibody levels and inflammation in your thyroid gland may be reduced
The autoimmune process destroying your thyroid may be slowed or stopped
If your thyroid is enlarged (goiter), the size of your gland may be reduced
The treatment may prevent you from progressing to overt hypothyroidism