What is the TSH value?
The abbreviation TSH stands for thyroid-stimulating hormone, also known as thyrotropin. This hormone is produced in the pituitary gland (hypophysis), more precisely in the anterior lobe of the pituitary gland. When required, the hormone is released into the blood to stimulate hormone production in the thyroid gland.
The TSH value therefore reflects the function of the thyroid gland: higher values are measured when hormone production in the thyroid gland needs to be stimulated because the blood levels of the thyroid hormones thyroxine (T4) and triiodothyronine (T3) are too low.
This is referred to as a TSH basal value determination if the TSH concentration for the test is not artificially stimulated or slowed down by the administration of other hormones. If the TSH basal value is normal, normal thyroid function can be assumed.
It is important to know that the TSH value also fluctuates naturally: TSH drops during the day until the afternoon and then rises again until midnight. In addition, the value is usually higher in children and older people.
The TSH value is determined if an overactive thyroid (hyperthyroidism) or an underactive thyroid (hypothyroidism) is suspected.
It is also routinely measured before all examinations in which patients are given an iodine-containing X-ray contrast medium. Such an agent may only be administered if thyroid function is not impaired.
The TSH concentration in the blood is also determined before treatment with iodine-containing medication (e.g. for wound care) and before major procedures involving general anesthesia.
TSH value: desire to have children and pregnancy
If a woman who is trying to conceive does not become pregnant, a measurement of the TSH concentration in the blood is also essential. This is because a malfunction of the thyroid gland can impair the function of the reproductive organs and lead to (temporary) infertility.
TSH normal values
TSH values are normally given in units of µIU/l or mIU/l, i.e. quantity or units per volume. Depending on the age of the patient, the following thyroid normal values apply:
|
age |
TSH normal value |
|
1st week of life |
0.71 – 57.20 µIU/ml |
|
1 week to 1 year |
0.61 – 10.90 µIU/ml |
|
1 to 3 years |
0.60 – 5.80 µIU/ml |
|
adults |
0.27 – 4.20 µIU/ml |
These standard values vary depending on the laboratory, as different measurement methods can lead to different results. For example, the upper TSH limit for adults can be between 2.5 and 5.0 mIU/l.
People over the age of 70 generally have higher TSH normal values. However, there are no studies to indicate a specific reference range for older people. TSH levels are also altered during pregnancy. Narrower and lower reference values apply:
|
Third trimester of pregnancy |
TSH normal value |
|
1st trimester |
0.1 – 2.5 mIU/l |
|
2nd trimester |
0.2 – 3.0 mIU/l |
|
3rd trimester |
0.3 – 3.0 mIU/l |
When is the TSH value too low?
- Autonomy of the thyroid gland (hormone production uncoupled from the control circuit)
- Graves’ disease
- Early stage of Hashimoto’s thyroiditis (autoimmune-related chronic thyroid inflammation).
If both the TSH value and the blood values for the thyroid hormones are low, this means that the pituitary gland produces too little TSH of its own accord (and not because T3 or T4 are elevated). Possible reasons for this:
- Dysfunction of the anterior lobe of the pituitary gland (anterior pituitary insufficiency), for example due to a tumor, radiotherapy or brain surgery (secondary hypothyroidism)
- rarely: Dysfunction in the hypothalamus: as a superordinate brain region, it controls the release of TSH from the pituitary gland via the messenger substance TRH (tertiary hypothyroidism)
When is the TSH value too high?
If the concentration of TSH basal is elevated while the blood levels of thyroid hormones are low, this may be due to primary hypothyroidism: In this case, there is a disorder in the thyroid gland itself, due to which too little T3 and T4 are produced. To counteract this, the pituitary gland releases increased amounts of TSH. Possible causes of primary hypothyroidism are
- chronic thyroid inflammation, especially advanced Hashimoto’s thyroiditis
- Surgical partial or complete removal of the thyroid gland
Certain medications can also cause TSH levels to rise excessively. These include, for example, so-called dopamine antagonists such as haloperidol. These are active substances that are used in the treatment of psychiatric illnesses, for example.
Changed TSH value: what to do?
If the TSH basal value is increased or decreased, the next step is to determine the concentrations of thyroid hormones. Depending on whether it is hypothyroidism or hyperthyroidism, the treatment will vary.
If it is suspected that the pituitary gland is dysfunctional, a TRH test is usually carried out. TRH is a superordinate hormone from the hypothalamus. It stimulates the pituitary gland to release TSH. This allows the doctor to determine whether the disorder is actually in the pituitary gland or in the hypothalamus. If the suspicion is confirmed, further hormone tests are necessary, as well as a magnetic resonance imaging (MRI) of the skull.
