Understanding Thyroid Gland Diagnostic Tests

Diagnostic testing for thyroid health involves evaluation of blood work

Thyroid Gland Review

The thyroid gland is a vitally important hormonal gland, which mainly works for body’s metabolism. It is located in the front part of the neck below the voice box and is butterfly-shaped. The functions of the thyroid gland include the production of the thyroid hormones triiodothyronine (T3) and tetraiodothyronine, also called thyroxine (T4).

The thyroid hormones have a variety of different functions: They regulate metabolism, growth and maturation of the human body.  There you will also find more information on thyroid hyperfunction and hypofunction, and the signs and symptoms of these conditions.

The production of the thyroid hormones is regulated by the pituitary gland (hypophysis). The pituitary gland produces the thyroid-stimulating hormone (TSH), which not only stimulates the production of thyroid hormones, but also influences the size of the thyroid gland. TSH production, in turn, is inhibited by the thyroid hormones. The system can be compared to a thermostat, which makes sure that room temperature is kept at a set value. This is why the concentration of thyroid hormones in the blood usually is fairly constant. 

There are different tests to check the functioning of the thyroid gland. We will now explain which ones there are and what they are used for.

Palpation

What is a palpation of the thyroid gland?

After talking with you, the examination the doctor usually does first will be a palpation: he or she will touch the neck with their hands, paying attention to what the thyroid gland feels like and whether it might have enlarged.

What do the results mean?

An enlarged thyroid – also called goiter or struma – can indicate a lack of iodine but with thyroid function still in normal range. Yet it can also be a sign of thyroid hyperfunction (too much thyroid hormone production), or of thyroid hypofunction (too little thyroid hormone production). Palpable nodules can also be a sign of a thyroid function problem. But neither enlargement nor nodules necessarily mean that the functioning of the thyroid gland is impaired.

Blood Tests

What is a blood test for thyroid hormones?

The thyroid gland continually releases a certain amount of hormones into the blood. So a blood test can be used to determine the amounts of hormones produced by the thyroid gland.

The blood test measures TSH and the thyroid hormones triiodothyronine (T3) and thyroxine (T4). A change in the TSH level can be an early detector for a thyroid function problem. This is why often, as a first step, only TSH is measured. If the TSH level in the blood is higher or lower than normal, the thyroid hormones T4 and T3 are also measured. Because most thyroid hormones are bound to certain blood proteins and only free hormones (which are not bound to proteins) act in the body, nowadays only the so-called “free thyroid hormones” (FT3 and FT4 – with “F” standing for “free”) are measured.

Thyroid antibodies are measured when looking for the cause of a thyroid function problem. Apparently, if our immune system wrongly regards the body’s own thyroid gland cells as foreign substances, it produces thyroid antibodies.

Another hormone produced by the thyroid gland is calcitonin. Its blood level is not routinely measured. If the calcitonin level in the blood is higher than usual, this can indicate a certain type of thyroid gland cancer, however, if such a disease is already suspected.

What do the results mean?

If the amount of thyroid hormones T3 and T4 is too high or too low, there is an imbalance between the thyroid hormones needed by the body and the amount of thyroid hormones available.

A blood test can measure the following substances:

• Thyroid-stimulating hormone (TSH): A TSH level that is higher than normal indicates thyroid hypofunction (hypothyroidism), because the pituitary gland produces more TSH in order to stimulate the thyroid gland to produce thyroid hormones. If, on the other hand, there is very little TSH in the blood, this can indicate thyroid hyperfunction (hyperthyroidism). The pituitary gland then tries to balance the excess amount of thyroid hormones by producing less TSH, in order to not stimulate the thyroid gland any more.
• Free triiodothyronine (FT3) and free thyroxine (FT4): Levels of free thyroid hormones in the blood that are higher than normal can indicate a hyperfunction. If there are not enough thyroid hormones, this can be a sign of a thyroid hypofunction.
• Thyroid antibodies: The concentration of different thyroid antibodies is raised in certain thyroid disorders, where the body’s immune system works against the thyroid tissue. These disorders include so-called Hashimoto’s thyroiditis and Grave’s disease. A low level of antibodies is associated with a variety of diseases such as an inflammation of the thyroid gland (thyroiditis), type 1 diabetes or rheumatoid arthritis.
• Calcitonin: The calcitonin level is usually raised in a certain type of thyroid cancer. But it also plays an important role in calcium and bone metabolism and can also be changed in other diseases.

Many drugs, if they are taken long-term, can also influence the concentration of TSH and thyroid hormones. And pregnancy can also change the hormone concentration in the blood.

Substances influencing thyroid measurements include:

• Acetylsalicylic acid or ASA (ASS in German)
• Cortisone
• St John's wort
• Certain water pills containing furosemide
• Thyroid medications

For this reason, it is important to inform your doctor about any drugs you take.

Thyroid Ultrasound

What is thyroid ultrasound?

An ultrasound examination (sonography) is used to obtain a picture of the thyroid. To do the examination, a small amount of jelly is put on the transducer of the ultrasound scanner, which is then moved over the neck. This examination uses sound waves that are sent into the part of the body to be examined. Depending on the type of tissue, these sound waves are sent back with different intensities or not at all, or are deviated. The sound waves that are sent back are turned into a spatial image on the monitor of the ultrasound device, so that changes in the tissue and the size of the thyroid gland can be seen. An ultrasound examination has no known adverse effects or risks.

What do the results mean?

In an ultrasound examination, enlargement of the thyroid gland can be seen. Changes in the tissue – like cysts or age-related alterations – can also be detected. If the thyroid gland is larger than normal, this may be associated with a thyroid hypofunction or hyperfunction. To say for sure whether the thyroid gland really produces too many or not enough hormones, it is necessary to do an additional blood test, however.

If nodules are detected in the ultrasound examination, it might be useful to do other examinations like a thyroid scan or, in some cases, magnetic resonance tomography (MRT).

Thyroid Scan

What is a thyroid scan?

A thyroid scan (or thyroid scintigraphy) is used to obtain a picture of the thyroid metabolism. The examination uses a weakly radioactive substance that is injected into an arm vein. The bloodstream carries this substance into every part of the body, but it is the thyroid gland that will take up most of it. Depending on how intensely or how weakly the thyroid gland is working, a larger or lesser amount of the substance will build up in the thyroid tissue. The thyroid scan can create a picture of the distribution and the amount of this weakly radioactive substance. This picture is called a scintigram.

It may be necessary to stop taking certain drugs before having a thyroid scan, for example thyroid medications. It is therefore important to talk to your doctor before the examination about which drugs you take.

A scintigraphy can have adverse effects. In rare cases, the needle can damage blood vessels or nerves, or the puncture can become inflamed. Allergic reactions, particularly against the substance injected, are possible.

What is more, people who have this examination done are exposed to radiation. Only small amounts of radioactive substances are used, however, and they will decay in the body in a few days.

What do the results mean?

A thyroid scan examines the activity of the thyroid gland: The more the thyroid gland works, the more blood goes through it and the more of the injected substance builds up in the tissue. On the image, the active areas have brighter or different colors than the non-active ones.

Depending on how much of the injected substance builds up, the areas are called cold nodules or hot nodules.

If less substance with a radioactive tracer is built up in one area, this nodule is called “cold”. Compared to the surrounding area, the metabolism of this tissue is less active. In most cases, a cold nodule indicates harmless changes in the tissue. Even if there is less metabolism in the area of the nodule, this usually does not lead to a lack of thyroid hormones, because the remaining tissue makes up for it by producing more hormones. In very rare cases, a cold nodule can also be a thyroid tumor.

In the “hot” nodules, which produce many hormones, on the other hand, more substance with the radioactive tracer builds up – the metabolism is more active. From a certain size, hot nodules can lead to thyroid hyperfunction. 

Fine Needle Aspiration

What is a thyroid fine needle aspiration?

For a thyroid fine needle aspiration a fine, thin needle is put into the thyroid tissue to withdraw tissue or fluid. It is usually not necessary to use an anesthetic, because the examination is not more unpleasant than having a normal blood sample taken from the arm. For better orientation, doctors often additionally use an ultrasound scanner.

In rare cases, the place where the needle was put in can become bruised or inflamed after the examination. If you take medication that stops the blood from clotting (anticoagulants), it is important to talk to your doctor about whether it is necessary to stop taking it before having fine needle aspiration.

What do the results mean?

Thyroid fine needle aspiration can give additional clues about whether the changes are benign or malignant (cancerous). The cells of the tissue samples taken are tested in a laboratory. A fine needle can also be used to empty fluid-filled cysts. It is also possible to detect an inflammation of the thyroid tissue.

Next planned update: June, 2014. You can find out more about how our health information is updated here.

References

• Bruhn HD, Fölsch UR, Schäfer H. LaborMedizin – Indikationen, Methodik und Laborwerte – Pathophysiologie und Klinik.Stuttgart: Schattauer-Verlag. 2008.
• Cooper DS. Hyperthyroidism. Lancet 2003; 362: 459-468.
• Dayan CM. Interpretation of thyroid function tests. Lancet 2001; 357: 619-624.
• Kharlip J, Cooper DS. Recent developments in hyperthyroidism. Lancet 2009; 373: 1930-1932.
• Mehanna HM, Jain A, Morton RP, Watkinson J, Shaha A. Investigating the thyroid nodule. BMJ 2009; 338: 705-709.

SOURCE: German Institute for Quality and Efficiency in Health Care (IQWiG).

Created: May 24, 2011  Last Update: July 6, 2011.