Exams and Tests

A thorough medical history and physical exam are the first steps in diagnosing hypothyroidism or mild (subclinical) hypothyroidism. If the results lead your doctor to suspect you have hypothyroidism or subclinical hypothyroidism, you will have tests to confirm the diagnosis.

Blood tests are always used to confirm a diagnosis of hypothyroidism or mild hypothyroidism. The tests used most often are:

• Thyroid-stimulating hormone (TSH) assay.
• Thyroxine (T4) measurement.

If the above tests are not normal, the antithyroid antibody test may determine whether you have the autoimmune disease Hashimoto's thyroiditis, in which the body's defense system attacks the thyroid gland.

On rare occasions, the following imaging tests may be used to evaluate a thyroid gland that appears to be abnormal during physical examination:

• Thyroid ultrasound
• Thyroid scan and radioactive iodine uptake (RAIU) test

A computed tomography (CT) scan or magnetic resonance imaging (MRI) of the hypothalamus or pituitary gland may be done to look for any changes in these areas of the brain.

Early detection

Because of the possibility of intellectual disability in infants with hypothyroidism, every state in the United States tests newborns for hypothyroidism. If your baby was not born in a hospital, or if you believe your baby may not have been tested, talk to your health professional. Screening tests for hypothyroidism are not always accurate. Even if test results show no problem, watch your child for symptoms of hypothyroidism, such as poor appetite, not gaining weight, and dry skin.

Some health professionals now recommend routine testing for people at risk for hypothyroidism, including:

• People age 35 and older. The American Thyroid Association guidelines recommend that screening begin at age 35 and continue every 5 years thereafter.⁶
• People with one or more close relatives who have or had hypothyroidism.
• People with conditions associated with Hashimoto's thyroiditis, including Addison's disease, rheumatoid arthritis, pernicious anemia, and type 1 diabetes.
• Pregnant women. In pregnant women known to have hypothyroidism, tests should be done at regular intervals to determine whether the dosage of thyroid hormone medicine is adequate.
• Women who are having symptoms of hypothyroidism after pregnancy (postpartum hypothyroidism), such as depression, memory and concentration problems, or thyroid enlargement (goiter). Women who have had hypothyroidism during or after pregnancy should be retested if they become pregnant again.

Not all experts agree on whether to recommend widespread screening for hypothyroidism. Some groups say there is not enough evidence of benefit to recommend screening for everyone. But people who are at high risk—women older than 60 and anyone with a family history of thyroid disease or who has other autoimmune diseases—may want to be screened.^{7, 5}