What is TSH?
TSH (thyroid-stimulating hormone) is one of the most important laboratory values for assessing thyroid health. Whether underactive or overactive – changes in TSH levels can cause numerous symptoms and indicate various diseases. In this article, you will learn everything you need to know about TSH: its functions, normal values, causes of abnormalities, common symptoms, and diagnostic options.
Table of Contents
- What is TSH?
- What does TSH do?
- What is the difference between TSH and T3/T4?
- What are normal TSH levels?
- Causes of high TSH
- Causes of low TSH
- Symptoms of high TSH
- Symptoms of low TSH
- What can I do if my TSH value is too high or too low?
What is TSH?
TSH stands for thyroid-stimulating hormone and is produced in the pituitary gland. It stimulates the thyroid gland to produce the thyroid hormones T3 (triiodothyronine) and T4 (thyroxine). These hormones enter the body’s cells via the bloodstream and regulate metabolism. Thyroid hormones are essential for energy balance, growth, and mental well-being. When thyroid hormone levels are high, TSH production decreases. When T3 and T4 levels are low, TSH production increases. This interplay maintains hormonal balance (Cleveland Clinic, 2022).
What does TSH do?
TSH controls the production of T3 and T4. These hormones influence, among other things:
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Heart rhythm
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Fat metabolism
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Protein breakdown
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Bone growth
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Brain development
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Sugar absorption
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Oxygen consumption
A high TSH level usually indicates an underactive thyroid (hypothyroidism), in which metabolism is slowed. A low TSH level often points to an overactive thyroid (hyperthyroidism), in which metabolism is accelerated (Endocrine Society).
What is the difference between TSH, T4, and T3?
Although TSH and thyroid hormones are related, they perform different functions:
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TSH is produced in the pituitary gland and regulates the production of thyroid hormones.
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T4 (free thyroxine) is a precursor hormone and is partially converted into T3 in the body’s cells.
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T3 (free triiodothyronine) is the biologically active form and regulates energy expenditure as well as numerous metabolic processes.
What are normal TSH levels?
Generally, a normal TSH level is 0.4 – 4.0 mU/L (American Thyroid Association). Reference values can vary depending on the laboratory, age, sex, or pregnancy.
What does high TSH mean?
A high TSH level means that the pituitary gland is producing more TSH because the thyroid gland is producing too few hormones. This indicates hypothyroidism (underactive thyroid).
What does low TSH mean?
A low TSH level usually indicates that the thyroid is producing too many hormones (hyperthyroidism). Medications or certain life stages, such as pregnancy, can also lead to low TSH levels.
What causes high TSH?
Common causes include:
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Hashimoto’s thyroiditis (an autoimmune disease in which the immune system attacks the thyroid gland)
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Inflammation of the thyroid after childbirth
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Thyroid surgery
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Radiation treatment in the neck area
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Medications (e.g., lithium, iodine-containing drugs)
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Treatment with radioactive iodine
Women, older adults, and people with a family history of thyroid disease are at higher risk.
What causes low TSH?
The most common cause is Graves’ disease (Morbus Basedow), an autoimmune disorder that stimulates the thyroid gland to overproduce hormones. Other causes include:
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Goiter (enlargement of the thyroid gland with increased hormone production)
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De Quervain’s thyroiditis (a painful, temporary inflammation of the thyroid)
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Painless thyroiditis (non-painful inflammation of the thyroid)
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Medications or hormonal influences (e.g., pregnancy)
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?
The most important conditions include:
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Hashimoto’s thyroiditis
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Graves’ disease (Morbus Basedow)
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Goiter (struma)
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De Quervain’s thyroiditis
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Other thyroid inflammations
Source: Nederlands Huisartsen Genootschap
TSH Test with Homed-IQ
An at-home TSH test is useful if you want to know whether your thyroid levels are within the normal range. The blood sample is collected with a simple finger prick. Your sample is then analyzed in a certified laboratory under medical supervision.
The Homed-IQ Thyroid Blood test measures your TSH level, giving you a good picture of your thyroid function – conveniently from home.
What can I do if my TSH value is too high or too low?
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Overactive thyroid (hyperthyroidism): Treatment options include medication, radioiodine therapy, or surgery.
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Underactive thyroid (hypothyroidism): Treatment involves thyroid hormone replacement (e.g., levothyroxine). The effects usually become noticeable after a few weeks, and many symptoms improve significantly.
Important: Always discuss abnormal test results with your general practitioner or an endocrinologist. Only medical examinations can provide an accurate diagnosis and ensure the right treatment.
