Hypothyroidism is a common condition, which affects the thyroid gland. Appropriate diagnosis of hypothyroidism depends on:
- Signs and symptoms, medical history, risk factors and family history.
- Findings of physical exam.
- Blood tests for TSH and free T4 or free T4 index.
Medical history and physical examination: These form the first step in diagnosing hypothyroidism. Your doctor will ask you questions regarding changes in your health and your symptoms. Some other questions that your doctor may ask are:
- If you had thyroid surgery or ever had radiation given to your neck to treat cancer.
- What are the medications that you are taking as some medications can cause hypothyroidism such as amiodarone, lithium, interferon alpha, interleukin-2 etc.
- If anyone in your family has thyroid disease (family history of the disease increases your chances of developing hypothyroidism).
During physical exam, the doctor will check your thyroid gland, look for changes in skin such as dry skin, swelling of legs, slower reflexes and a slower heart rate. If findings of physical examination or signs and symptoms suggest that you have hypothyroidism or subclinical hypothyroidism, your doctor will do tests to confirm the diagnosis.
Laboratory tests: The two blood tests that are used to diagnose hypothyroidism are TSH (thyroid-stimulating hormone) test and T4 tests.
- TSH (thyroid-stimulating hormone) test: This is the most important and sensitive test to diagnose hypothyroidism. TSH is a hormone that control synthesis of thyroid hormone T4 in the body and the level of TSH is influenced by T4 level in the blood. When less T4 is made by the thyroid gland more TSH is present in the blood. If the level of TSH is abnormally high, you have hypothyroidism i.e. your thyroid gland is being asked to make more T4 as the level of T4 is less in the blood.
- T4 tests: The test measures the level of thyroid hormone in your blood. If the level of T4 is low, it confirms hypothyroidism. Tests to measure the level of free T4 and the free T4 index may also be done. These tests measure the amount of unattached T4 that is available to get into the cells.
- Other tests: Some other tests that may be done include tests for anti-thyroid peroxidase (anti-TPO) antibodies, imaging tests of the brain such as CT scan or MRI scan.