Thyroid Peroxidase Antibodies (TPO)

The Thyroid Peroxidase Antibodies (TPOAb) test detects antibodies directed against thyroid peroxidase, an enzyme involved in the production of thyroid hormones. The presence of TPO antibodies is commonly associated with autoimmune thyroid disorders such as Hashimoto's thyroiditis and Graves' disease.

1. What Is TPO?

• Thyroid peroxidase (TPO) is an enzyme in the thyroid gland that plays a key role in the synthesis of thyroid hormones (T3 and T4).

• In autoimmune thyroid diseases, the immune system mistakenly attacks TPO, impairing thyroid function.

• The TPOAb test identifies these autoantibodies in the blood.

2. Why Is the TPOAb Test Performed?

This test is used to:

• Diagnose autoimmune thyroid conditions such as Hashimoto’s thyroiditis and Graves’ disease.

• Investigate the cause of hypothyroidism or hyperthyroidism.

• Monitor individuals with known thyroid disease or risk factors (e.g., family history, other autoimmune diseases).

• Assess risk of thyroid dysfunction during pregnancy or postpartum.

3. TPO Antibodies Reference Range

• Normal: < 35 IU/mL (international units per milliliter)

• Positive (elevated): ≥ 35 IU/mL — indicates the presence of thyroid autoimmunity.

• Reference ranges may vary by laboratory.

4. Interpreting TPOAb Results

🔹 Positive TPO Antibodies:

• Suggest an autoimmune thyroid disorder such as Hashimoto’s thyroiditis or Graves’ disease.

• Even in euthyroid individuals (normal thyroid hormone levels), a positive result may predict future thyroid dysfunction.

🔹 Negative TPO Antibodies:

• Makes autoimmune thyroid disease less likely, though not impossible.

• Other tests (e.g., TSH, Free T4, TGAb) may still be needed to evaluate thyroid health.

5. What Can Affect TPOAb Levels?

• Autoimmune diseases (e.g., type 1 diabetes, rheumatoid arthritis, lupus)

• Pregnancy (levels may rise postpartum)

• Thyroid surgery or radioactive iodine therapy

6. How Is the Test Performed?

• A blood sample is drawn from a vein.

• No fasting is required for this test.

7. When to See a Doctor

🚨 Contact your healthcare provider if you:

• Experience symptoms of thyroid dysfunction (e.g., fatigue, weight changes, cold intolerance, swelling in the neck).

• Have a family or personal history of autoimmune disease.

• Are pregnant and have risk factors for thyroid dysfunction.

🔹 Key Takeaways

✅ TPO antibodies are markers of autoimmune thyroid disease.

✅ A positive test supports the diagnosis of Hashimoto’s or Graves’ disease.

✅ Early detection allows for monitoring and management of thyroid function over time.