The doctor will perform a physical exam and ask about your symptoms and medical/family history. The exam may reveal a goiter (enlarged thyroid), slow reflexes, dry skin, slow and hoarse speech, and/or a large tongue.

Your doctor may also do the following tests:

Blood Tests —Blood tests measure the level of thyroid hormone and thyroid antibodies. The diagnosis of hypothyroidism is made if the serum level of thyroid stimulating hormone (TSH) is elevated, and the levels of serum free T4 and free T3 are in the low or normal range. These results mean that the thyroid gland is not active enough.

The presence of thyroid antibodies may also signal autoimmune hypothyroidism, such as Hashimoto's thyroiditis . In some cases, thyroid antibodies attacking the thyroid gland cause hypothyroidism.

Some blood tests performed for other reasons may raise suspicions about hypothyroidism and should be followed up, for example, blood tests that show high cholesterol, anemia, or low sodium.