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Thyroid Terminology 101

Important terms associated with hypothyroidism to help you better understand the disorder.
Thyroid Terminology 101
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If you are diagnosed with a thyroid disorder or disease, you’ve read or heard unfamiliar terms. It’s easy to not fully understand what everything means.

We’ve put together this brief thyroid glossary of the most common terms associated with thyroid gland-related medical conditions—primarily terms associated with hypothyroidism.


The body has proteins called antibodies that are produced to attack invaders, like viruses. Some antibodies attack healthy tissue by mistake. When antibodies attack the thyroid gland, hormone production can be stunted, thus resulting in hypothyroidism.

Antithyroid Agents

Antithyroid agents (also called anti-thyroid drugs) are a class of medications that are also referred to as thionamides, including methimazole and propylthiouracil, which inhibit organification of iodide. This can slow thyroid hormone production and peripheral thyroid effects.

Anti-thyroid Microsomal Antibodies Test

Another test often given for thyroid disease is the anti-thyroid microsomal antibodies test. These forms of antibodies have the ability to attack thyroid cells. The presence of these antibodies suggests potential autoimmune destruction of the thyroid. A small number  of people with this condition present negative results but still have autoimmune thyroid destruction.


Apoptosis (also Apoptotic) is a description of pre-programmed cell death that has the capacity to destroy specific cells without causing damage to surrounding cells.

Autoimmune Disease

An autoimmune disease is a disease caused as a result of a malfunction or defect in the body’s immune system. Rather than protecting the body, a healthy part of the body is attacked and destroyed. Having an autoimmune disease may be a risk factor for individuals with hypothyroidism.

Free T3 Test

The Free T3 Test measures the level of triiodothyronine (T3) in the bloodstream. Paloma Health includes this biomarker in our at-home thyroid test kit, to accompany the TSH test for more comprehensive results.

Free T4 Test

The Free T4 test measures the level of Free T4 in the bloodstream. Paloma Health includes this biomarker in our at-home thyroid test kit, to accompany the TSH test for more comprehensive results. If free T4 levels are low, it may be indicative that hypothyroidism is present.


Goiter is an abnormal enlargement of the thyroid gland—sometimes seen as a bulge in the front of your neck. Goiter could be caused by an iodine deficiency, developing when the thyroid enlarges in an effort to obtain more iodine from the bloodstream. It could also be influenced by family history or certain medications.

Hashimoto’s Disease

Hashimoto’s disease is an autoimmune disorder in which antibodies attack your thyroid gland, leading to chronic inflammation. It is the most common cause of hypothyroidism in the United States.

Graves Disease

Graves Disease is an autoimmune disorder that causes hyperthyroidism, or overactive thyroid.


Hypothyroidism is when the thyroid gland is underactive. Your thyroid hormone production drops and your body processes slow down and change. Since your body needs a certain amount of these hormones to function properly, this condition can affect many different systems in your body.


Iodine is a vital nutrient in the body and essential for normal thyroid hormone production, which controls the body’s metabolism. When thyroid stimulating hormone (TSH) is secreted from the pituitary gland in the brain, it increases the thyroid’s uptake of iodine and stimulates the synthesis and release of Thyroxine (T4) and Triiodothyronine (T3).


Liothyronine is sometimes used to treat hypothyroidism. This drug contains the synthetic form of one thyroid hormone, T3. Cytomel is the most commonly available brand-name version of liothyronine.


Levothyroxine is used to treat hypothyroidism, replacing the thyroid hormone that is normally made by the thyroid gland. Levothyroxine contains the synthetic form of one thyroid hormone, T4. Levothyroxine is the most commonly prescribed thyroid hormone replacement drug. Unithroid, Synthroid, Tirosint, Levoxyl, and Euthyrox are brand names for the synthetic T4 hormone.


The thyroid helps to regulate metabolism. Metabolism is the body’s ability to break down oxygen and calories to convert to energy.


Myxedema is a severe form of hypothyroidism that can occur when the condition is left untreated, long-term. It is rare and often presents itself with symptoms such as extreme sensitivity to cold as well as slowed bodily function. Myxedema can be life-threatening and requires emergency medical attention.

Pituitary Gland

The pituitary gland is a tiny organ located at the base of the brain. Often called the “master gland” of the body, it is responsible for several other hormone glands in the body, including the secretion of thyroid stimulating hormone (TSH).

Synthetic Thyroid Supplements

Synthetic thyroid supplements are the gold standard treatment for hypothyroidism. These supplements are man-made, but they are a complete replica of the T4 that is naturally produced and released by the body’s thyroid.

Thyroid Gland

The thyroid is the butterfly-shaped gland at the base of your neck. It’s job it to make hormones—most notably, T3 and T4—that regular you body’s energy use, along with many other important functions.  As part of the endocrine system, the thyroid gland makes and stores hormones that help regulate the body’s metabolism in the form for blood pressure, blood temperature, and heart rate. When your thyroid hormone production drops, your body processes slow down and change. This is hypothyroidism, and underactive thyroid.

Thyroid Hormone Replacement Therapy

The basic idea of hypothyroid treatment is the daily ingestion of hormones to make up for the lack of hormones produced by an underactive thyroid. Treatment popularly includes a synthetic form of T4 hormone, but it could also require the administration of T3 hormone.

Thyroid Stimulating Hormone (TSH)

TSH is a hormone produced in the pituitary gland in the brain. This hormone regulates the amount of Thyroxine (T4) and Triiodothyronine (T3) produced by the thyroid gland.


Thyroiditis is an inflammation of the thyroid gland, which can adversely impact the gland’s ability to regulate hormones. Thyroiditis can lead to permanent destruction of the thyroid.

Thyroxine (T4)

Thyroxine is the main hormone that is produced in and secreted by the thyroid gland. Without enough of T4 (and its counterpart T3), the body’s metabolism slows down. T4 and T3 are in charge of your body’s energy usage. T4 is mostly inactive (called a storage hormone); it’s primary function is to transport T3 to the proper organs in your body.

Triiodothyronine (T3)

Triiodothyronine is the active thyroid hormone that works at the cellular level to help with the delivery of oxygen and energy to cells, tissues, and glands throughout the body. The body must convert T4 into T3 to be used by cells. Without enough T3, the metabolism slows down.

TSH Test

While many labs only look at Thyroid Stimulating Hormone (TSH) as the initial line of testing to determine if a patient has hypothyroidism, Paloma Health believes it is critical to also measure Free Triiodothyronine (fT3), Free Thyroxine (fT4) and TPO Antibodies.

We make every attempt to ensure this information is accurate, and if you require a more detailed understanding of medical language or test results, please consult with your thyroid doctor.

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Katie Wilkinson

Katie Wilkinson, previously serving as the Head of Content and Community at Paloma Health, fervently explores the nexus between healthcare and technology. Living with an autoimmune condition, she's experienced firsthand the limitations of conventional healthcare. This fuels both her personal and professional commitment to enhancing patient accessibility to superior care.

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