From the Guidelines
Anti-thyroid peroxidase (anti-TPO) antibody is highly suggestive of Hashimoto's thyroiditis but not absolutely confirmatory on its own. A diagnosis of Hashimoto's thyroiditis typically requires a combination of clinical features, thyroid function tests, and antibody testing. Anti-TPO antibodies are present in about 90-95% of patients with Hashimoto's thyroiditis, making them a sensitive marker for the disease. However, these antibodies can also be found in other autoimmune thyroid conditions and occasionally in healthy individuals (especially older adults and pregnant women). 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 1, which found that the risk of developing overt hypothyroidism was 4.3% per year in individuals with anti-TPO antibodies, compared to 2.6% per year in antibody-negative individuals. For a more definitive diagnosis, doctors often consider the presence of anti-TPO antibodies along with:
- Clinical symptoms (such as fatigue, weight gain, cold intolerance)
- Physical examination findings (like an enlarged thyroid gland)
- Thyroid function tests showing hypothyroidism (elevated TSH and/or low free T4) In some cases, thyroid ultrasound or even a thyroid biopsy might be performed to confirm the diagnosis, particularly if there are suspicious nodules. The presence of anti-TPO antibodies is clinically significant as it indicates autoimmune thyroid disease and can help predict progression to overt hypothyroidism in patients with subclinical disease, as noted in 1.
From the Research
Anti-Thyroid Peroxidase Antibody in Hashimoto's Thyroiditis
- The presence of anti-thyroid peroxidase (anti-TPO) antibodies is a common feature of Hashimoto's thyroiditis, but it is not exclusive to this condition 2, 3, 4, 5.
- Studies have shown that anti-TPO antibodies can be found in individuals without thyroid disease, with a frequency ranging from 8.4% to 43% 4, 5.
- The level of anti-TPO antibodies can decrease in patients with Hashimoto's thyroiditis who are taking levothyroxine, but it may not become negative in all patients 2.
- High levels of anti-TPO antibodies (>1300 IU/mL) may indicate multifocal papillary thyroid cancer in patients with Hashimoto's thyroiditis, and support total thyroidectomy 6.
Diagnostic Value of Anti-TPO Antibodies
- Anti-TPO antibody assay by monoclonal antibody-assisted RIA appears to be more sensitive and specific for thyroid autoimmune diseases than anti-microsomal antibody determination by passive hemagglutination 5.
- The presence of anti-TPO antibodies is not sufficient to confirm a diagnosis of Hashimoto's thyroiditis, as it can be found in other conditions and in healthy individuals 4, 5.
- A combination of clinical, laboratory, and imaging findings is necessary to establish a diagnosis of Hashimoto's thyroiditis 2, 3, 6.
Association with Inflammation and Symptoms
- Elevated thyroid antibodies, including anti-TPO antibodies, are positively associated with inflammation and multiple extrathyroidal symptoms in patients with Hashimoto's thyroiditis 3.
- The level of anti-TPO antibodies is inversely correlated with health-related life quality and positively correlated with pro-inflammatory factors and severity of symptoms 3.