Understanding thyroid tests

The thyroid gland is a vital endocrine (hormone-producing) gland. It is located at the front of the neck, below the voice box, and is butterfly-shaped.

The thyroid gland produces the thyroid triiodothyronine (T3) and thyroxine (T4), among other things. These thyroid have various functions: They are responsible for the metabolism, growth and development of the body.

The pituitary gland (hypophysis) makes sure that the thyroid is always making the right amount of . It releases a hormone called TSH (thyroid-stimulating hormone) into the bloodstream to increase the production of thyroid . Too many thyroid in the bloodstream causes the pituitary gland to make less TSH. The system can be compared to a thermostat, which makes sure that the room temperature is kept at a certain value. So the concentration of thyroid in the blood is usually fairly constant.

There are different tests and examinations to measure the concentration of the thyroid and the TSH in the blood and to determine the size and the texture of the thyroid tissue.

Palpation of the thyroid gland

In this examination, the doctor carefully feels your neck where your thyroid gland is, usually from behind you. It is easier to feel the thyroid from this position. They will pay attention to what the thyroid gland feels like and whether it is bigger than usual.

What do the results tell us?

An enlarged thyroid is also called a goiter. The most common cause of a goiter is iodine deficiency. The thyroid gland often continues to work normally.

But a thyroid can also become enlarged for other reasons. It may be that many benign (non-cancerous) nodules develop in it, or it could be caused by the thyroid being overactive (hyperthyroidism) or underactive (hypothyroidism).

So doctors will only be able to tell so much after feeling the thyroid gland. Further testing is needed in order to find out what the cause is any whether there could be a problem with the functioning of the gland.

Blood tests

The thyroid gland constantly releases a certain amount of into the blood. So a blood test can be done to determine the amounts of it is making.

Blood tests can measure the levels of TSH and the thyroid triiodothyronine (T3) and thyroxine (T4). Abnormal TSH levels may be an early sign of thyroid problems. For this reason, it is common to only measure the TSH level at first. If the TSH level in the blood is higher or lower than normal, the levels of the thyroid T3 and T4 are also measured.

If doctors think that an autoimmune reaction is causing problems in the functioning of the thyroid, they will look at the levels of thyroid antibodies. These are antibodies made by the that bind to the thyroid tissue. This can cause in the thyroid gland, stop it from functioning or simulate it to make too many .

Some parts of the thyroid make another hormone called calcitonin. The level of calcitonin in the blood is usually only measured if there is reason to believe that someone has a certain type of thyroid cancer that increases the amount of calcitonin.

What do the results tell us?

The levels of the following substances can help to find out what is causing problems in the production of the thyroid :

  • Thyroid-stimulating hormone (TSH): High TSH levels are a sign of an underactive thyroid (hypothyroidism). They show that the pituitary gland is trying to stimulate the thyroid gland to produce thyroid . Very low TSH levels in the blood may be a sign of an overactive thyroid (hyperthyroidism). The pituitary gland then produces less TSH, in order to stop “telling” the thyroid gland to make more .
  • Free triiodothyronine (FT3) and free thyroxine (FT4): High levels of free thyroid in the blood can indicate a hyperfunction. If they are low, this can be a sign of a thyroid hypofunction.
  • Thyroid antibodies: The concentration of thyroid antibodies in the blood is higher in certain disorders where the body’s immune system attacks the thyroid gland. These include Hashimoto’s disease and Graves’ disease.
  • Calcitonin: Calcitonin levels are usually higher in a certain type of thyroid cancer. But high levels of calcitonin can also be a sign of other diseases, such as kidney failure. Calcitonin levels play an important role in and bone metabolism too.

The concentration of TSH and thyroid in the blood can also be influenced by the long-term use of certain medications. These medications include:

  • Acetylsalicylic acid (the drug in medicines like Aspirin)
  • Steroids
  • St. John's wort
  • Certain diuretic medications containing furosemide
  • Thyroid medications

Because of this, it’s important to let your doctor know about any medications you are using before having a blood test.

Thyroid ultrasound

In a thyroid ultrasound (sonography), sound waves are sent to the thyroid gland. Depending on the type of tissue they bounce off there, the sound waves are then sent back with different intensities or not at all. To do the examination, a small amount of gel is put on the “head” (transducer) of the ultrasound device, which is then moved over the neck. The sound waves that bounce off the thyroid tissue are measured by the transducer and turned into a two-dimensional or spatial image that is shown on a screen.

What do the results tell us?

The ultrasound image shows the doctor whether the thyroid gland is bigger than normal (enlarged). It can't show whether the enlarged gland is making too many or two few . That is why a blood test typically needs to be done too.

Changes in the tissue – like nodules or cysts – can also be seen in ultrasound images. If nodules (lumps) are discovered, other examinations may be done to find out more about them. These include a thyroid scan or (MRI).

Thyroid scan (scintigraphy)

A thyroid scan (thyroid scintigraphy) is done to see how active the thyroid gland is (how many it is producing in which parts of the thyroid). Before doing the scan, a slightly radioactive substance is injected into an arm vein. This substance travels around the body in the bloodstream, but most of it is absorbed by the thyroid gland. The more active the individual areas of the thyroid gland are working, the more of the substance they absorb. The thyroid scan image shows how much of the radioactive substance has been absorbed in which area. This image is called a scintigram.

It may be necessary to stop taking certain drugs, such as thyroid medications, before having a thyroid scan. Because of this, it’s important to let your doctor know about any medications you are taking before the scan.

In rare cases, the needle might damage blood vessels or nerves, or the skin at the site of injection may become infected during a thyroid scan. Allergic reactions, particularly to the injected substance, are possible.

People are exposed to a small amount of radiation during the scan. Only very small amounts of radioactive substances are used, though, and they are broken down in the body within a few days without causing any harm.

What do the results tell us?

Thyroid scans allow us to look at how evenly the thyroid gland is working or whether certain areas are especially active. Those are referred to as “hot” nodules. Hot nodules are benign (non-cancerous), but they could be the cause of an overactive thyroid. Areas that produce fewer compared to the rest of the thyroid, or none at all, are referred to as "cold." nodules. Most cold nodules are also benign. In very cases, though, they are caused by a malignant (cancerous) thyroid tumor.

Tissue sample (biopsy)

A technique called fine needle aspiration is typically used to take a sample of the thyroid tissue. The doctor inserts a very fine, hollow needle into the part of the thyroid gland that needs to be tested in order to remove tissue or fluid.

It is usually not necessary to numb the area with an anesthetic because it’s not more unpleasant than having a blood sample taken from your arm.

In rare cases, the place where the needle was inserted may become bruised or infected. If you take medication that stops blood from clotting (anticoagulants), it’s important to talk to your doctor about whether you should stop taking it before the procedure. Sometimes the aspiration needs to be repeated or the doctor needs to use a larger needle.

What do the results tell us?

After the tissue sample has been examined in a laboratory, doctors can see whether the thyroid tissue is inflamed or has undergone malignant changes.

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Deutsche Gesellschaft für Allgemeinmedizin und Familienmedizin (DEGAM). Erhöhter TSH-Wert in der Hausarztpraxis (S2k-Leitlinie). AWMF-Registernr.: 053-046. 2023.

Jameson JL, Mandel SJ, Weetman AP. Disorders of the Thyreoid Gland. In: D. L. Kaspers, S. L. Hauser, J. L. Jameson et al. (Ed). Harrison's Principles of Internal Medicine. McGraw-Hill Education; 2015.

National Institute for Health and Care Excellence (NICE). Thyroid disease: assessment and management. 2019.

Pschyrembel Online. 2024.

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Updated on May 28, 2024

Next planned update: 2027


Institute for Quality and Efficiency in Health Care (IQWiG, Germany)

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