How is thyroid disease diagnosed?

Sometimes, thyroid disease can be difficult to diagnose because the symptoms are easily confused with those of other conditions. You may experience similar symptoms when you are pregnant or aging and you would when developing a thyroid disease. Fortunately, there are tests that can help determine if your symptoms are being caused by a thyroid issue. These tests include:

  • Blood tests.
  • Imaging tests.
  • Physical exams.

Blood tests

One of the most definitive ways to diagnose a thyroid problem is through blood tests. Thyroid blood tests are used to tell if your thyroid gland is functioning properly by measuring the amount of thyroid hormones in your blood. These tests are done by taking blood from a vein in your arm. Thyroid blood tests are used to see if you have:

  • Hyperthyroidism.
  • Hypothyroidism.

Thyroid blood tests are used to diagnose thyroid disorders associated with hyper- or hypothyroidism. These include:

The specific blood tests that will be done to test your thyroid can include:

  • Thyroid-stimulating hormone (TSH) is produced in the pituitary gland and regulates the balance of thyroid hormones — including T4 and T3 — in the bloodstream. This is usually the first test your provider will do to check for thyroid hormone imbalance. Most of the time, thyroid hormone deficiency (hypothyroidism) is associated with an elevated TSH level, while thyroid hormone excess (hyperthyroidism) is associated with a low TSH level. If TSH is abnormal, measurement of thyroid hormones directly, including thyroxine (T4) and triiodothyronine (T3) may be done to further evaluate the problem. Normal TSH range for an adult: 0.40 - 4.50 mIU/mL (milli-international units per liter of blood).
  • T4: Thyroxine tests for hypothyroidism and hyperthyroidism, and used to monitor treatment of thyroid disorders. Low T4 is seen with hypothyroidism, whereas high T4 levels may indicate hyperthyroidism. Normal T4 range for an adult: 5.0 – 11.0 ug/dL (micrograms per deciliter of blood).
  • FT4: Free T4 or free thyroxine is a method of measuring T4 that eliminates the effect of proteins that naturally bind T4 and may prevent accurate measurement. Normal FT4 range for an adult: 0.9 - 1.7 ng/dL (nanograms per deciliter of blood)
  • T3: Triiodothyronine tests help diagnose hyperthyroidism or to show the severity of hyperthyroidism. Low T3 levels can be observed in hypothyroidism, but more often this test is useful in the diagnosis and management of hyperthyroidism, where T3 levels are elevated. Normal T3 range: 100 - 200 ng/dL (nanograms per deciliter of blood).
  • FT3: Free T3 or free triiodothyronine is a method of measuring T3 that eliminates the effect of proteins that naturally bind T3 and may prevent accurate measurement. Normal FT3 range: 2.3 - 4.1 pg/mL (picograms per milliliter of blood)

These tests alone aren’t meant to diagnose any illness but may prompt your healthcare provider to do additional testing to evaluate for a possible thyroid disorder.

Additional blood tests might include:

  • Thyroid antibodies: These tests help identify different types of autoimmune thyroid conditions. Common thyroid antibody tests include microsomal antibodies (also known as thyroid peroxidase antibodies or TPO antibodies), thyroglobulin antibodies (also known as TG antibodies), and thyroid receptor antibodies (includes thyroid stimulating immunoglobulins [TSI] and thyroid blocking immunoglobulins [TBI]).
  • Calcitonin: This test is used to diagnose C-cell hyperplasia and medullary thyroid cancer, both of which are rare thyroid disorders.
  • Thyroglobulin: This test is used to diagnose thyroiditis (thyroid inflammation) and to monitor treatment of thyroid cancer.

Talk to your healthcare provider about the ranges for these thyroid blood tests. Your ranges might not be the same as someone else’s. That’s often alright. If you have any concerns or worries about your blood test results, talk to your provider.

Imaging tests

In many cases, taking a look at the thyroid itself can answer a lot of questions. Your healthcare provider might do an imaging test called a thyroid scan. This allows your provider to look at your thyroid to check for an increased size, shape or growths (nodules).

Your provider could also use an imaging test called an ultrasound. This is a diagnostic procedure that transmits high-frequency sound waves, inaudible to the human ear, through body tissues. The echoes are recorded and transformed into video or photographic images. You may think of ultrasounds related to pregnancy, but they are used to diagnose many different issues within your body. Unlike X-rays, ultrasounds do not use radiation.

There’s typically little or no preparation before your ultrasound. You don’t need to change your diet beforehand or fast. During the test, you’ll lie flat on a padded examining table with your head positioned on a pillow so that your head is tilted back. A warm, water-soluble gel is applied to the skin over the area that’s being examined. This gel won’t hurt your skin or stain your clothes. Your healthcare provider will then apply a probe to your neck and gently move it around to see all parts of the thyroid.

An ultrasound typically takes about 20 to 30 minutes.

Physical exam

Another way to quickly check the thyroid is with a physical exam in your healthcare provider’s office. This is a very simple and painless test where your provider feels your neck for any growths or enlargement of the thyroid.

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