How is Hyperthyroidism Diagnosed?

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Your thyroid, a small, butterfly-shaped gland, has an important job: to help oxygen and energy reach every organ, tissue, gland, and cell in your body. According to the American Thyroid Association’s 2016 Guidelines, around 1.2 percent of the population has hyperthyroidism. Getting a diagnosis of hyperthyroidism — an overactive thyroid — can be challenging. But you can help ensure a thorough assessment by following key steps, including self-assessment, a medical history, review of your symptoms, clinical examination by a practitioner, blood tests, and imaging tests. Let’s review these steps in the process of getting a hyperthyroidism diagnosis.

Self-assessment

Assessing your risk factors and symptoms for hyperthyroidism is an important first step. Here are some important factors that raise the possibility that you may be hyperthyroid:

  • A family or personal history of autoimmune disease
  • A lump or enlargement in your neck
  • Unexplained symptoms such as fatigue, weight loss, anxiety, insomnia, or among others
  • Being in a period of hormonal transition, such as pregnancy, postpartum, perimenopause, or postmenopausal
  • Being a current or former cigarette smoker

Note that testing for hyperthyroidism is not included in routine physicals or blood work. You will need to request an evaluation from your practitioner.

Medical history

At your visit, your practitioner should review your medical history, with special attention to:

  • A family history of thyroid disease, especially in first-degree relatives (parents, siblings, children) and female relatives
  • A family or personal history of autoimmune disease
  • Any past episodes of thyroid disease that you may have experienced, such as a temporary thyroiditis or postpartum thyroiditis
  • Any history of trauma to your neck
  • Any medications you are taking, with particular notice of those known to cause hyperthyroidism, such as Interferon Beta-1b, Interleukin-4, immunosuppressants, antiretroviral drugs, lithium, or monoclonal antibody (Campath-1H)

Clinical examination

Your practitioner should conduct a thorough clinical examination of your thyroid, including the following evaluations:

  • Feeling your neck to detect any thyroid enlargement (goiter) and/or nodules, which can be signs of hyperthyroidism.
  • Check your reflexes. Typically, the doctor will use a small rubber mallet to see if your reflexes are hyperresponsive, a sign of hyperthyroidism.
  • Check your heart rate. A fast heart rate, and/or arrhythmia and palpitations, can point to hyperthyroidism.
  • Check your blood pressure. High blood pressure can be a sign of hyperthyroidism.
  • Check your weight to look for weight loss since your last visit, as this can be a sign of hyperthyroidism.
  • Look for milaria rash on your face, changes in your fingers and nails, and rashes on your shins that are common in hyperthyroidism.
  • Examine your eyes for any bulging/protrusion, redness, dryness, or swelling that can point to hyperthyroidism or thyroid eye disease.

Review of symptoms

Your practitioner should review your key symptoms with you. It may be helpful to bring a one-page checklist summarizing your most problematic symptoms. Even better: Consider sending the checklist before your appointment, in case your practitioner has time to review it in advance.

Blood tests

According to the American Thyroid Association, a number of blood tests can factor into the diagnosis of hyperthyroidism.

Thyroid Stimulating Hormone (TSH): The TSH test measures a pituitary hormone that acts as a messenger to push the thyroid gland to produce more thyroid hormone. TSH levels go down when you are hyperthyroid, as the pituitary is trying to slow down thyroid hormone production. The reference range for TSH typically is from .50 to 4.5. Levels below the .50 lower end of the range are considered hyperthyroid.

Free Thyroxine (Free T4) Test: Free T4 measures the storage hormone, thyroxine, which is converted into triiodothyronine (T3) in order to be used by the body. The reference range for free T4 is 0.8 - 1.8 ng/dL Free T4 levels that are above the reference range are indicative of hyperthyroidism.

Free Triiodothyronine (Free T3) Test: Free T3 measures the available amount of circulating triiodothyronine — the active thyroid hormone. The reference range for free T3 is 2.3- 4.2 pg/mL. Free T3 levels that are above the reference range are indicative of hyperthyroidism.

Thyroid Stimulating Immunoglobulins (TSI) Test: The main cause of hyperthyroidism is Graves’ disease, an autoimmune disease.In Graves’ disease, antibodies are produced that overstimulate the thyroid to produce excess thyroid hormone, resulting in hyperthyroidism. The TSI test measures the antibodies found in Graves’ disease. TSI are found in 75 to 95% of people with Graves' disease.

Imaging tests

The key imaging test used in diagnosing hyperthyroidism is the radioactive iodine uptake (RAI-U) test. This test involves taking a pill with a very small dose of radioactive iodine. Several hours after taking the pill, an x-ray is conducted to view the gland’s uptake of the iodine. If you are hyperthyroid, the uptake will be elevated. The RAI-U test can also help identify whether nodules are “toxic” and are producing thyroid hormone.

Other imaging tests used to pinpoint a hyperthyroidism diagnosis, identify structural issues with your thyroid, or identify the underlying cause of your hyperthyroidism include:

  • A CT scan, known colloquially as a “CAT scan,” which can help to visualize thyroid enlargement or atrophy, irregular shape, and detect larger thyroid nodules
  • Magnetic resonance imaging (MRI), which can provide information about the shape and size of your thyroid, and identify enlargement or atrophy
  • Ultrasound of your thyroid, to look for and evaluate liquid-filled and solid thyroid cysts and nodules, and identify thyroid enlargement or atrophy

See more helpful articles:

The Risks for and Symptoms of Hyperthyroidism

The Causes of Hyperthyroidism

How Are Hyperthyroidism and Graves' Disease Treated?