Thyroid Peroxidase (TPO) is an enzyme found in the thyroid gland, an organ in the neck. This enzyme plays a role in the production of thyroid hormones, which regulate various bodily functions including metabolism, growth, and development. Measuring TPO levels is a common way to assess thyroid health and identify potential issues.
Understanding Thyroid Peroxidase (TPO)
TPO serves a specific function in the thyroid gland’s hormone production. It facilitates the addition of iodine to a protein called thyroglobulin, a chemical step necessary for creating the thyroid hormones thyroxine (T4) and triiodothyronine (T3). These hormones are then released into the bloodstream to influence processes throughout the body.
The immune system, which protects the body, can sometimes mistakenly target its own tissues. In the thyroid, it might produce proteins called TPO antibodies that mistakenly attack TPO. The presence of these antibodies indicates an autoimmune response directed at the thyroid gland, which can disrupt its normal function.
Defining Normal TPO Levels
Normal TPO levels can vary among laboratories due to testing differences. Generally, a TPO antibody level below 9 IU/mL or 34 IU/mL is considered within the normal range. These levels suggest TPO antibodies are either not detectable or not significant.
A normal TPO level indicates that the immune system is not actively producing antibodies against the thyroid peroxidase enzyme. However, these reference ranges are guidelines. A single TPO level provides only one piece of information and does not offer a complete picture of overall thyroid health.
What Abnormal TPO Levels Indicate
Elevated TPO levels suggest the presence of TPO antibodies, indicating autoimmune activity targeting the thyroid gland. High TPO antibody levels are a strong indicator of autoimmune thyroid conditions. The most common condition associated with elevated TPO antibodies is Hashimoto’s thyroiditis, an autoimmune disorder that can lead to an underactive thyroid (hypothyroidism). In Hashimoto’s, the immune system gradually damages the thyroid, impairing its ability to produce hormones.
Elevated TPO antibodies can also be found in individuals with Graves’ disease, an autoimmune condition that causes an overactive thyroid (hyperthyroidism). While less common than in Hashimoto’s, their presence in Graves’ disease also points to an autoimmune attack on the thyroid. Very high TPO antibody levels (for example, above 500 IU/mL) can suggest an increased risk of developing hypothyroidism in the future, even if current thyroid hormone levels are normal.
Navigating Your TPO Test Results
Discuss your TPO test results with a healthcare provider. TPO levels are just one component of a comprehensive thyroid assessment. Healthcare providers typically consider TPO levels alongside other thyroid hormone tests, such as Thyroid Stimulating Hormone (TSH) and Free T4, as well as your individual symptoms and medical history.
The presence of high TPO antibodies does not always mean immediate treatment is necessary. Rather, it can indicate a predisposition to or ongoing autoimmune activity in the thyroid that may require monitoring over time. This monitoring helps to track any changes in thyroid function and determine if and when intervention might be beneficial. It is important to avoid self-diagnosis or self-treatment based solely on TPO test results.