ThyroidWomen's Health

TSH Levels

Written by

Lauren Dobischok
16 May, 2022

Medically checked article All HOMED-IQ content is reviewed by medical specialists

The thyroid is a butterfly-shaped gland located in the neck. This gland is important for the production of certain hormones that control the body’s metabolism. During a thyroid disorder, the gland can either work too slowly or too quickly, which can affect many different body systems and cause a number of unpleasant symptoms. Homed-IQ’s Thyroid Blood Test measures the amount of TSH and other key thyroid hormones in your blood, giving insight into whether your thyroid is functioning properly or not.

Table of Contents

What is TSH?

Thyroid Stimulating Hormone (TSH) is a hormone that is produced by the pituitary gland. The pituitary gland is located at the bottom of the brain, behind the nose and sinuses. TSH directs the thyroid gland to produce thyroid hormones. These hormones are then released into the bloodstream, where they can reach different cells and moderate body functions such as metabolism.

The amount of TSH the body produces is directly related to the amount of thyroid hormones in the body. When thyroid hormone levels are high, TSH production decreases. When thyroid hormone levels are low, TSH production increases. Since the level of TSH in the blood is influenced by the amount of thyroid hormones produced, abnormally high or low TSH levels can be an important clue that there is a problem with the thyroid. If the thyroid is overactive and producing too much thyroid hormone (hyperthyroidism), TSH levels will be low. If the thyroid is underactive and not producing enough thyroid hormone (hypothyroidism), TSH levels will be high.

What does TSH do?

TSH stimulates the thyroid gland to produce the thyroid hormones thyroxine (T4) and triiodothyronine (T3). These hormones affect how your body uses energy, which is also known as metabolism. T4 and T3 have an effect on several organs and body systems, including the heart, muscles, bones, nervous system, and intestines. Thyroid hormones impact:

  • Heart rhythm
  • Fat Burning
  • Protein breakdown
  • Bone growth
  • Brain development
  • Absorption of sugars
  • Oxygen consumption

Source: Endocrine Society

What is the difference between TSH, T4, and T3?

While TSH, T3, and T4 are all hormones related to the thyroid, they all have different functions.


Thyroid Stimulating Hormone (TSH) is produced in the pituitary gland, which is located in the brain. TSH stimulates the thyroid to produce and release hormones (T3 and T4).


Triiodothyronine (T3) is one of the two major thyroid hormones. It is the most active thyroid hormone, affecting many organs and body processes such as metabolism, energy consumption, growth, and brain development. While the thyroid produces a small amount of T3, most of it is created from the conversion of T4 into T3 in body’s tissues.


Free T3 (FT3) is the form of triiodothyronine not bound to protein in the blood. This form of T3 can freely enter the body’s tissues when needed. Since this hormone of T3 is readily available for the body to use, FT3 is often included in a thyroid function blood test. When it is measured with bound (inactive) T3, it is called total T3. 


Thyroxine (T4) is the second major hormone produced by the thyroid. It is produced in larger quantities by the thyroid and is mostly converted into T3. Although T4 is less active in the body than T3, it acts as a reservoir that the body can convert to T3 as needed.


Free T4 (FT4) is the form of thyroxine not bound to protein in the blood. This form of T4 can freely enter the body’s tissues when needed. Since FT4 is the form of the hormone that is free for your body to use, it is often the type of T4 that is tested when checking thyroid function.

What are normal TSH levels?

Generally, a normal TSH level is 0.4 – 4.0 mU/L (American Thyroid Association). This reference range may differ slightly between laboratories. If a thyroid test shows that your TSH level is within the reference range, it means you have a normal TSH level.

What does high TSH mean?

High TSH usually occurs when the thyroid is not producing enough T3 and T4, prompting the pituitary gland to produce more TSH. The medical term for this is hypothyroidism, or an underactive thyroid. Damage to the thyroid, autoimmune conditions, and other injuries can impair the thyroid’s ability to produce hormones, causing hypothyroidism.

What does low TSH mean?

Low TSH usually occurs when the thyroid is producing too much T3 and T4, prompting the pituitary gland to produce less TSH. This is called hyperthyroidism, or an overactive thyroid. Hyperthyroidism is often caused by autoimmune diseases, growths on the thyroid, or inflammation.

In rare causes, tumours on the pituitary gland can cause abnormal TSH production, leading to either hyper- or hypothyroidism.

What causes high TSH?

An important cause of high TSH or an underactive thyroid is Hashimoto’s disease. Hashimoto’s disease is an autoimmune disorder in which the immune system mistakenly attacks thyroid cells. This damages the thyroid, causing it to make lower amounts of hormones over time and eventually even stop. In addition to this autoimmune disease, there are a number of other causes for high TSH:

  • Problems with the immune system
  • Inflamed thyroid gland after childbirth
  • Thyroid surgery
  • Radiation of the neck
  • Medicines containing iodine
  • Medicines containing lithium
  • Treatment with radioactive iodine

You are more likely to develop an underactive thyroid if this condition runs in your family. The risk also increases after childbirth, especially in the first year after. Women and elderly people are also more likely to develop a thyroid condition. 

What causes low TSH?

The most common cause of low TSH or an overactive thyroid is Graves’ disease. This autoimmune condition causes the body to develop antibodies against the thyroid gland. The thyroid responds by producing more hormones. Other causes also include:

  • Thyroid surgery: removal of all or part of the thyroid gland
  • Quervain’s disease: painful inflammation of the thyroid gland (non-chronic)
  • Thyroiditis: non-painful inflammation of the thyroid gland

Source: Isala, 2022

Symptoms of high TSH

High TSH and its associated hypothyroidism causes a variety of symptoms impacting the entire body. Symptoms of an underactive thyroid include::

  • Getting cold quickly
  • Weight gain
  • Fatigue
  • Slower heart rate
  • Constipation
  • Hair loss
  • Pale skin
  • Swollen eyelids
  • Thyroid swelling
  • Voice changes
  • Irregular periods

Source: Thuisarts, 2019

Symptoms of low TSH

Low TSH and its associated hyperthyroidism can cause a variety of symptoms due to too much thyroid hormones. Symptoms of an overactive thyroid include:

  • Heart palpitations
  • Trembling
  • Sweating
  • Anxiety
  • Fatigue
  • Intestinal problems
  • Weight loss
  • Warm skin
  • Bulging eyes
  • Blurred vision
  • Irregular periods
  • Enlarged thyroid (goiter)

Source: Cleveland Clinic, 2022

Are there any diseases related to abnormal TSH levels?

There are several diseases associated with abnormal TSH levels, such as Hashimoto’s disease, Graves’ disease, goiters, Quervain’s disease, and thyroiditis (Nederlands Huisartsen Genootschap).

TSH testing

A TSH test can give an indication of how well your thyroid is working. Abnormal TSH levels may indicate either an over- or underactive thyroid that requires further treatment. Homed-IQ’s Thyroid Test allows users to check their TSH, FT3, and FT4 levels from home. Using this home test, you can measure your TSH levels without visiting the doctor. This is done through a simple finger prick that is mailed to one of Homed-IQ’s certified laboratories for analysis.

What can I do if my TSH value is too high or too low?

An overactive thyroid (hyperthyroidism) can be treated in different ways. The first step of treatment is visiting your doctor. Your GP may prescribe medication to suppress thyroid hormone production, treatment with radioactive iodine, or advise surgery to remove the thyroid. An underactive thyroid (hypothyroidism) is usually treated by taking daily thyroid hormone replacement medications.

Discover your TSH value

Do you experience symptoms that could indicate thyroid problems and would like to check your TSH level? Try Homed-IQ’s Thyroid Test to test the levels of key thyroid hormones from home. Please note: if are experiencing severe symptoms, we recommend contacting your GP immediately.

About the author

Lauren Dobischok

Lauren is a health scientist and science communicator currently living in the Netherlands. Originally from Canada, she completed a Research Master’s in Health Sciences at the Netherlands Institute of Health Sciences at Erasmus University Rotterdam (NIHES) with a specialisation in epidemiology. Prior to her master’s degree, she completed a Bachelor’s degree in Health Sciences at Simon Fraser University. With a background in public health, her goal is to create accurate scientific content that is easy to understand and empowers people to make informed decisions. Within Homed-IQ, Lauren works as a Product Developer and Content Lead, working closely with physicians and scientists on medical devices for Homed-IQ’s new products and written communications.