Thyroid Peroxidase Antibody (TPO)

Thyroid Peroxidase Antibody (TPO)

The Thyroid Peroxidase Antibody (TPO) test is a blood test used to detect antibodies that target thyroid peroxidase, an enzyme involved in the production of thyroid hormones. The presence of TPO antibodies can indicate autoimmune thyroid conditions, such as Hashimoto’s thyroiditis or Graves’ disease, and may help explain thyroid dysfunction when other tests are inconclusive.

How it works: A blood sample is drawn from a vein, usually from the arm. The sample is analyzed in a laboratory to measure the level of thyroid peroxidase antibodies. Elevated levels suggest an autoimmune process affecting the thyroid gland, even if thyroid hormone levels are currently normal.

When you might need this test: It is commonly ordered if you have symptoms of thyroid disease (such as fatigue, weight changes, cold intolerance, hair loss, or mood changes) or if you have a family history of autoimmune thyroid disease. It is also used to monitor autoimmune thyroid conditions over time or to assess risk in individuals with abnormal thyroid function tests but unclear etiology.

Understanding the results:

• Positive or elevated TPO antibodies usually indicate an autoimmune process affecting the thyroid. This does not diagnose a specific condition on its own but supports autoimmune thyroid disease as a potential cause.
• Low or undetectable TPO antibodies make an autoimmune thyroid cause less likely but do not completely rule it out.
• Results should be interpreted in the context of other thyroid tests, such as TSH, Free T4, and Free T3, as well as clinical symptoms.

What to expect after the test: Most people have little to no downtime. You may experience a brief pinprick at the puncture site, followed by minor bruising or soreness. Results are typically available within a few days and are reported as an antibody level with a reference range provided by the laboratory.

Limitations: A positive TPO antibody result indicates autoimmunity but does not specify disease severity, current thyroid status, or prognosis. Some individuals with autoimmune thyroid disease may have normal TPO antibody levels at certain times. The test is most informative when used alongside other thyroid function tests and clinical assessment.

Who should consider testing: Adults and, in some cases, adolescents with suspected thyroid dysfunction or a family history of autoimmune thyroid disease. Discuss with a healthcare provider to determine if testing is appropriate for your symptoms and medical history.

Sample collection and processing: A licensed clinician collects a blood sample, typically from a vein in the arm. The sample is sent to a laboratory for assay using immunoassay techniques to quantify TPO antibody concentration.

Accessibility and insurance: Availability and coverage vary by location and insurer. Check with your healthcare provider and insurance plan for specific details about testing, costs, and any required referrals.