Testing is done to evaluate the health of the thyroid, diagnose Hashimoto thyroiditis, and monitor treatment.
To determine whether the thyroid is functioning properly and for monitoring thyroid function and hormone production, one or more of the following blood tests may be done:
- Thyroid-stimulating hormone (TSH) — typically elevated in hypothyroidism
- Free T4 — often decreased in primary hypothyroidism
- Total or Free T3 — sometimes decreased but may be within the normal reference range, so is not as useful as free T4
Additional tests may be used to detect autoantibodies directed against the thyroid and to help diagnose Hashimoto thyroiditis:
- Anti-thyroid peroxidase antibody (anti-TPO, see Thyroid Antibodies) — this test detects the presence of autoantibodies against a protein found in thyroid cells. A high value usually indicates autoimmune damage to the thyroid due to disorders such as Hashimoto thyroiditis and Graves disease.
- Antithyroglobulin antibody (TgAb) — if positive, may indicate Hashimoto thyroiditis; while thyroglobulin antibodies are often positive, they are not as sensitive or specific as anti-TPO so they are not routinely ordered.
People with a very mild form of Hashimoto thyroiditis may not have thyroid antibodies present in their blood.