Blood Tests

Think you have hypothyroidism? Get tested.

If you think you may have hypothyroidism, your doctor can order the following blood tests to measure your thyroid hormone levels and diagnose thyroid conditions.

The Free T3 and Free T4 tests measure the T3 and T4 that are carried in the blood and unattached to proteins. Most of the T4 and T3 in the body are attached to carrier proteins and not free-flowing. Since certain conditions, such as pregnancy and liver disease, can increase carrier protein concentrations, doctors will get a more accurate reading by assessing the levels of free T3 and T4.

Free Thyroxine (T4) – FT4 test.

This test measures the levels of thyroxine (T4) in your blood, since a low level could indicate hypothyroidism.

Free Triiodothyronine (T3) – FT3 test.

This test measures the levels of triiodothyronine (T3) in your blood, since a low level could indicate hypothyroidism.

Thyroid antibody test.

The immune system produces antibodies to protect us from foreign invaders. These antibodies are produced by white blood cells (lymphocytes) to destroy harmful attackers such as bacteria or viruses. People who suffer from hypothyroidism may produce antibodies (thyroid peroxidase and thyroglobulin) that also attack the body, specifically the thyroid gland. Positive levels of these antibodies found in the blood can indicate conditions such as Hashimoto’s thyroiditis or autoimmune thyroid disease.

TSH test.

In the early stages of hypothyroidism, your thyroid hormone levels may still be in the normal range. Therefore, doctors often rely on the TSH (thyroid-stimulating hormone) blood test for diagnosing hypothyroidism.

Patient Education – Endocrine Encyclopedia. (n.d.). UCLA Endocrine Surgery. Retrieved October 12, 2011 from
American Thyroid Association. (2005). Thyroid Function Tests [Brochure]. Retrieved from