What are anti-thyroid peroxidase antibodies (anti-TPO Abs)?

From the Guidelines

Anti-TPO antibodies are a crucial marker for autoimmune thyroid disease and should be considered in the diagnostic workup of patients with suspected thyroid dysfunction, particularly in those with type 1 diabetes, as their presence is predictive of thyroid dysfunction, most commonly hypothyroidism. Anti-TPO antibodies (anti-thyroid peroxidase antibodies) are autoantibodies that target thyroid peroxidase, an enzyme essential for thyroid hormone production. These antibodies are the most common marker for autoimmune thyroid disease, particularly Hashimoto's thyroiditis. When present in elevated levels, they indicate that the immune system is attacking the thyroid gland, which can lead to inflammation and gradual destruction of thyroid tissue. Testing for anti-TPO antibodies is typically done through a simple blood test, with normal levels generally below 35 IU/mL, though reference ranges may vary between laboratories. Elevated levels are found in approximately 90% of patients with Hashimoto's thyroiditis and about 70% of those with Graves' disease.

Key Points

• The presence of anti-TPO antibodies identifies an autoimmune etiology for thyroid dysfunction and predicts a higher risk of developing overt hypothyroidism, as seen in a study published in JAMA 1.
• According to a 2018 study published in Diabetes Care, consideration should be given to testing individuals with type 1 diabetes for antithyroid peroxidase and antithyroglobulin antibodies soon after diagnosis, and measuring thyroid-stimulating hormone concentrations at diagnosis when clinically stable or soon after glycemic control has been established 1.
• While the presence of these antibodies confirms autoimmune thyroid disease, treatment decisions are usually based on thyroid function tests (TSH, T3, T4) rather than antibody levels alone.
• There is no specific treatment to reduce antibody levels; instead, management focuses on addressing thyroid dysfunction with medications like levothyroxine for hypothyroidism.
• Regular monitoring of thyroid function is important for patients with positive anti-TPO antibodies, even if thyroid function is initially normal, as they have an increased risk of developing thyroid dysfunction over time. Some key considerations in the management of patients with anti-TPO antibodies include:
• Monitoring thyroid function tests regularly, ideally every 1-2 years, or sooner if symptoms suggestive of thyroid dysfunction develop 1.
• Being aware of the potential for thyroid dysfunction to impact glycemic control in patients with diabetes.
• Considering the presence of anti-TPO antibodies as a predictor of thyroid dysfunction, particularly in patients with type 1 diabetes.

From the Research

Anti-TPO Abs Overview

• Anti-thyroid peroxidase antibodies (TPO-Abs) are a type of autoantibody associated with autoimmune thyroid disease, particularly Hashimoto's thyroiditis 2, 3, 4, 5, 6
• TPO-Abs are detected in the serum of patients with Hashimoto's thyroiditis and are used as a diagnostic marker for the disease 2, 3, 4, 5

Clinical Significance

• The presence of TPO-Abs is associated with a 2 to 4-fold increase in the risk of recurrent miscarriages and preterm birth in pregnant women 2
• TPO-Abs are also associated with an increased risk of papillary thyroid cancer and thyroid lymphoma 2
• In patients with Hashimoto's thyroiditis, TPO-Ab levels decline in most patients taking levothyroxine, but after a mean of 50 months, TPO-Ab became negative in only a minority of patients 3

Determinants and Risk Factors

• Female sex and current smoking are determinants of TPO-Ab positivity and TPO-Ab detectability, respectively 6
• Higher age and all categories of alcohol consumption are associated with lower odds of TPO-Ab detectability 6
• TPO-Ab detectability is associated with a higher risk of overall, cancer-related, and cardiovascular mortality, particularly in men 6

Treatment and Management

• Levothyroxine treatment is commonly used to manage hypothyroidism in patients with Hashimoto's thyroiditis, and TPO-Ab levels may decline during treatment 3, 5
• The dose of levothyroxine used for treatment is based on the degree of preserved thyroid functionality and lean body mass, and usually ranges from 1.4 to 1.8 mcg/kg/day 2