Thyroid Function Tests Explained
Thyroid disorders affect more than 12 percent of the population in the U.S., according to the American Thyroid Association, with up to 60 percent of those people unaware of their condition. The thyroid is a hormone-producing gland that regulates body metabolism, which is the rate at which it uses energy. The hormones produced by the thyroid gland affect nearly every cell in the body and influence a wide range of critical bodily functions, which means that a poorly functioning thyroid can have serious and widespread consequences. Thyroid hormone function tests are used to detect thyroid disorders, helping to ensure that they can be diagnosed and treated before complications occur.
What is included in a thyroid panel?
What is included in a thyroid panel, also commonly called a thyroid function test or a thyroid hormone function test, varies to some extent according to the particular lab used for testing and the tests ordered. A basic thyroid panel will include measurements of TSH, as well as total T3 and T4 levels. Some thyroid panel packages also test levels of free T3 and T4, which are hormones that are not bound to other molecules in the bloodstream, and therefore freely available for various uses in the body. Other thyroid panels may include components that test hormone uptake or tests that look for indications of autoimmune activity or genetic defects that may affect thyroid function. These additional tests offer a more comprehensive and detailed picture of overall thyroid health and function.
Measures the amount of thyroid-stimulating hormone (TSH), T3 uptake, T4 and T7.
Measures the amount of thyroid-stimulating hormone TSH, Free T3, Free T4, T3 Uptake, T4 and T7
This Ayumetrix at home test kit may be used to asses the level of Thyroid function by testing hormones such as TSH, Free T3, Free T4, and TPO.
Measures T3 Uptake, T4 and T7
This test is used to measure the amount of Iodine in the blood.
Measures the amount of parathyroid hormone and calcium
Measures the amount of parathyroid hormone to evaluate parathyroid function
This test measures the level of Reverse T3, a metabolite of Thyroxine (T4).
Measures the amount of freely circulating triiodothyronine (T3) to evaluate thyroid function
Measures the amount of triiodothyronine, T3, to evaluate thyroid function
Measures the amount of free thyroxine (T4) to evaluate thyroid function
The Thyroglobulin Antibody blood test is used to measure the level of the thryoglobulin antibody in the blood to asses thyroid function.
Measures the amount of thyroid peroxidase (TPO) antibodies to help understand the cause of thyroid disorders
Measures T3 Uptake, T4 and T7
A TSI test measures the amount of thyroid stimulating immunoglobulin in your blood.
Measures the amount of thyroid-stimulating hormone (TSH) to evaluate thyroid function
The T4 test measures the level of a key thyroid hormone, T4, in the blood.
This test measures the levels of thyroid-stimulating hormone (TSH) and free thyroxine (T4) in the body.
Measures the amount of thyroid-stimulating hormone (TSH) and free thyroxine (T4) to evaluate thyroid function
What is the normal thyroid level?
Normal thyroid levels are not absolute numbers. Rather, having your thyroid tested means that your hormone levels will be compared to a "normal range". According to HealthLine, normal thyroid test results are as follows:
- TSH – Thyroid TSH that measures between 0.4 and 4.0 milli-international units per liter
- T3 – When tested, hormone T3 results should be between 100 to 200 nanograms per deciliter
- T4 – Normal range for this thyroid hormone is 4.5 to 11.2 micrograms per deciliter
How do you diagnose hypothyroidism?
Hypothyroidism, also commonly called under-active thyroid, is a disorder that occurs when the thyroid gland is not producing enough thyroid hormones, causing metabolism to slow. It may stem from problems with the thyroid gland itself, or with the pituitary gland which produces hormones that help regulate thyroid function. It is typically diagnosed via blood tests, usually after symptoms of hypothyroidism have been noted. These may include:
- Weight gain
- Facial puffiness
- Dry, brittle nails
- Dry, brittle hair and/or hair loss
- Slow heart rate
- Memory impairment
- Dry skin
- Increased sensitivity to cold
- In severe cases, coma
Often, when hypothyroidism is suspected, a TSH (thyroid stimulating hormone) test may be done first to evaluate TSH levels. TSH is secreted by the pituitary gland, and stimulates the thyroid gland to release thyroid hormones when levels drop in the bloodstream. If TSH levels are abnormally high, this can indicate that the thyroid is not responding adequately to repeated calls for more hormones. When this happens, a thyroid panel is typically done, which is a blood test that measures levels of TSH and thyroid hormones, called T3 and T4.
Once hypothyroidism is confirmed, additional testing is usually done to help determine the underlying causes of the condition. Common causes of an under-active thyroid include:
- Hashimoto's disease – an autoimmune disease that causes inflammation of the thyroid gland as the body's own immune system attacks the gland.
- Thyroid hormone resistance – a condition in which the body becomes unable to use thyroid hormones efficiently.
- Medications – certain medications can suppress thyroid activity.
- Thyroid nodules – These are growths, usually benign, that can develop on the thyroid gland to inhibit normal function.
- Thyroiditis – inflammation of the thyroid gland.
How do you test for hyperthyroidism?
Hyperthyroidism, also commonly called over-active thyroid, is a condition in which the thyroid gland is producing abnormally high amounts of thyroid hormones T3 and T4, speeding up the metabolism. Symptoms of this thyroid disorder can include:
- Excessive sweating
- Clammy skin
- Increased heat sensitivity
- Diarrhea and/or frequent elimination
- Fast or irregular heartbeat
- Weight loss
- Increased appetite
Testing for hyperthyroidism, typically done in response to the appearance of symptoms, is also done with blood tests. Often, a TSH test is the first to be done. When testing for hyperthyroidism, a low level of TSH is the marker of a potential problem, since there is no need for the pituitary gland to use TSH to call for more thyroid hormones when the bloodstream is already flooded with an excessive amount of T3 and T4. If low TSH is found, more testing, generally a thyroid panel blood test, is done to evaluate thyroid function in greater detail and help determine the underlying causes of the condition. Common causes of Hyperthyroidism include:
- Graves' disease – The most common cause of an over-active thyroid, Graves' disease is an autoimmune condition that results in overproduction of thyroid hormones as the immune system damages the thyroid gland.
- Thyroid nodules – Growths on the thyroid gland, most often non-cancerous, can contain hormone-producing cells, causing excessive production of T3 and T4.
If you suspect that you may be affected by a thyroid disorder, whether you have noticed some of the symptoms listed above or are concerned due to a family history of thyroid disease, getting tested is better done sooner than later. Should tested hormone levels yield results that are not within the normal range and a thyroid disorder is likely, pursuing medical treatment and care immediately is critical to maintaining your health and well-being. Why is it so important to take these steps? Because left untreated, thyroid disorders can lead to serious complications that can affect your health for life, including cardiovascular complications, cognitive impairments, infertility, nerve damage and much more – complications that are easily avoided by prompt testing, diagnosis and treatment.
Citations: American Thyroid Association https://www.thyroid.org/media-main/about-hypothyroidism/ HealthLine Normal TSH levels: http://www.healthline.com/health/tsh#results5 Normal T3 levels: http://www.healthline.com/health/t3#Preparation3 Normal T4 Levels: http://www.healthline.com/health/t4-test