Thyroid Testing Overview
Reviewed By: Dr. Kurt Kloss, MD
Last Reviewed Date: Feb 20, 2019
Last Modified Date: Feb 20, 2019
Published Date: Jul 29, 2017
Thyroid Function Tests Explained
Your thyroid is a small gland located in the front of your lower neck. The thyroid produces hormones that regulates your mood, energy levels, and metabolism, which is the rate at which your body uses energy. It produces two main hormones,T3 (triiodothyronine) and T4 (thyroxine).
Your thyroid cells also play a primary role in metabolizing iodine. When the cells bring together iodine and tyrosine, T3 and T4 are produced and released into the blood to control your digestion. When your thyroid is healthy and functioning well, it produces 80% T4 and 20% T3. When these are well functioning, a signal goes to the pituitary gland to turn down the production of thyroid-stimulating hormone (TSH). When the levels are low, the pituitary gland increases its production of TSH.
These hormones affect nearly every cell in your body and influence a wide range of critical bodily functions, which means that a poorly functioning thyroid can have serious and widespread consequences. 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.
Thyroid hormone function tests are used to detect thyroid disorders, helping to ensure that they can be diagnosed and treated before complications occur. View sample thyroid test results with lab variations, ranges and explanations.
Women might have thyroid problems without noticing any specific signs, especially at the onset of the disease. So, they are recommended to do the thyroid functions blood test at least every five years, starting the age of 35 years. Thyroid screening is essential for pregnant women and elderly.
What are the symptoms of thyroid problems in females?
When it comes to thyroid problems, studies show women to be eight times more likely than men to experience them, at some point of their lives. For your gland to be operating normally, your body needs to produce the adequate amount of thyroid hormones. If your numbers are below the normal levels; then, you have what is called “hypothyroidism”. If the levels are higher than normal; then, you have hyperthyroidism.
Hypothyroidism may show signs such as weight gain, depression and feeling low on energy. The sensation of being worn out is very common. One can take the example of hibernating animals. These have low thyroid hormones levels, which help them go into long sleep. Women with low thyroid activity do feel tired, despite the fact that they are sleeping more than others. If you have hyperthyroidism; then, your symptoms might include weight loss, feeling anxious, and tremors.
Women with hypothyroidism may experience many symptoms. For example, you may feel tired all the time with an increased sensitivity to cold. You can be constipated and tend to gain weight. Dry skin, puffy face, thinning hair and hoarseness are also symptoms of hypothyroidism. Other signs include:
- Muscle weakness
- High blood cholesterol levels
- Aches and pains in your muscles and joints
- Having irregular menstrual periods that are possibly heavier than normal
- Slow heart rate and depression
- Impaired memory and possibly an enlarged gland
For women who might have hyperthyroidism, symptoms are fairly different, starting with a sudden weight loss for no probable cause, having fast irregular heartbeats, tremor, having fast and more recurrent daily bowel movements, as well as feeling anxious, nervous and irritable. Some experience mood swings, feel very tired and develop a sensitivity to heat. An enlarged thyroid may lead to sleep problems. Finally, a woman might start witnessing thinning of her skin, thinning of her hair and even changes in her menstrual cycle.
For people who first get hyperthyroidism, they might feel a boost in their energy. As a result, their metabolic rate will be sped up. This will break down their body and they will end up feeling very tired. Hyperthyroidism is a progressive disease that develops slowly through the years. It is mainly caused by a disorder of the immune system. For women who are taking medications to regulate their blood pressure, such as beta blockers; they need to be aware that such pills can mask the symptoms associated with hyperthyroidism.
What is included in a basic 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.
What is included in a full thyroid panel?
A full or comprehensive panel of thyroid blood tests generally includes the following:
- T4: this is a hormone that is found in two forms. Part of the T4 hormone is freely circulating in the blood (FT4), available to be used by the body and its tissues. The other form is bound to proteins. Testing T4 cells can help you pinpoint what problems your thyroid gland is having. Higher than normal levels of FT4 indicate the presence of hyperthyroidism, while lower than normal levels indicate hypothyroidism.
- T3: this is a powerful hormone with four times the strength of T4. It controls almost every process in your body. It affects growth, metabolism, your heart rate as well as your body temperature. A full thyroid panel measures both the T3 Uptake and the free T3 (FT3).
- T7: a measure of T4 X T3 Uptake.
- TSH: the test measures the amount of TSH found in your blood. TSH is made by a gland found at the base of the brain. It regulates hormones produced by your thyroid. TSH levels are indicative of your thyroid status. Testing for TSH usually indicates the reason that is causing the thyroid to produce atypical amounts of hormones. It can also indicate whether there is an underproduction or overproduction of the hormones. Higher than normal levels of TSH can indicate hypothyroidism, while lower ones can indicate hyperthyroidism. Sometimes, it may be possible to have normal ranges of TSH; but, still have hypothyroidism.
- Thyroid Peroxidase (TPO) Antibodies, also called anti-thyroid microsomal antibodies test or anti-TPO.: the test measures the amount of thyroid peroxidase antibodies in the blood. Such antibodies are released by the immune system that have the ability to attack the thyroid. So, if these antibodies are found present in our blood; then, this could mean that thyroid cells are starting to get damaged. This could indicate hypothyroidism or an autoimmune thyroid disease such as Hachimoto thyroiditis or Grave’s disease.
What are normal thyroid hormone levels?
Normal thyroid levels are not absolute numbers. Rather, having your thyroid tested means that your hormone levels will be compared to a "normal range". Following is a guide that will tell you the normal ranges of each of the thyroid hormones:
- TSH: between 0.4 and 5.0 milli-international units per liter (m IU/L). But, many scientists and doctors believe that some individuals do have thyroid malfunctions with a TSH above 2.5 instead of 5.0
- T3: between 80 and 180 nanograms per deciliter (ng/dl)
- T4: between 4.6 and 12.0 micrograms per deciliter (ug/dl)
- Free T4: between 0.7 and 1.9 ng/dl
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 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. There are numerous other tests that can be done to detect abnormalities in thyroid function. Among them are the radioactive iodine uptake test and a thyroid scan. However, lab tests are the initial step in diagnosis.
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.
Thyroid Health Resources
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
Featured Tests And Packages
Measures the amount of thyroid-stimulating hormone (TSH) and free thyroxine (T4) to evaluate thyroid function
Measures the amount of thyroid-stimulating hormone (TSH), T3 uptake, T4, T7 and T3 Total.
Measures the amount of thyroid-stimulating hormone TSH, Free T3, Free T4, T3 Uptake, T4, T7, T3 Total and Thyroid Peroxidase Antibody (TPO).
Lab Tests (A-Z)
The Calcium, Ionized test is used to measure the free or unbound amount of calcium in the blood.
This test is used to measure the amount of Iodine in the blood. Too little or too high of Iodine in the blood may play an important contributing factor in thyroid disease and conditions.
Measures the amount of parathyroid hormone and calcium. PTH helps regulate calcium, vitamin D, and phosphorus levels in the blood and bones.
Measures the amount of intact parathyroid hormone to evaluate parathyroid function and abnormal calcium levels.
Measures the level of Reverse T3, that may inhibit the action of the T3 hormone.
Measures the amount of freely circulating triiodothyronine (T3) to evaluate thyroid function.
Measures the total amount of triiodothyronine, T3, to evaluate thyroid function.
Measures the amount of proteins in the blood that are capable of carrying a thyroid hormone.
Measures the amount of free thyroxine (T4) to evaluate thyroid function.
The Thyroglobulin Antibody test may be ordered when an individual has symptoms of a thyroid disorder or to evaluate treatment of thyroid cancer.
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 Thyroxine Total (T4 total) measures the level of a key thyroid hormone, T4, in the blood.
This TBG test is used to measure the level of Thyroxine-Binding Globulin in the blood to further evaluate thyroid function.
Measures the amount of thyroid-stimulating hormone (TSH) and free thyroxine (T4) to evaluate thyroid function
Thyroid Testing Locations By State
You can order blood work for thyroid health through either LabCorp or Quest Diagnostics. Combined they have over 3000 locations to choose from. The sates that are available for testing your thyroid are listed below.
You can also find available locations on our Lab Locator using a zip-code search.