What is thyrotropin (TSH) and what are the normal values?

What is Thyrotropin (TSH)?

Thyrotropin, known as TSH, is a key hormone produced in the pituitary gland, whose main function is to stimulate the activity of the thyroid gland. Its action enables the production of two essential thyroid hormones: thyroxine (T4) and triiodothyronine (T3). TSH is responsible for regulating the levels of T4 and T3 in the blood, allowing them to remain within a healthy range. Alterations in TSH levels can lead to imbalances in T4 and T3 concentrations, which can lead to the development of symptoms related to hyperthyroidism or hypothyroidism.

In some diseases, however, T4 and T3 levels can vary independently of TSH. Dysfunctions in the pituitary, the gland responsible for their production, can also affect TSH levels in the body.

Why is this analysis important?

The TSH test is a key tool for diagnosing and monitoring thyroid disorders, facilitating early identification and management of these conditions. At Ailin Health we provide you with an thyroid test to be carried out in the comfort of your own home, with a report and personalised medical recommendations.

No special preparation is necessary for this test, although it is essential to inform the physician of any medications in use, as some may interfere with TSH results. For patients receiving thyroid hormone treatment, it is usually recommended that the test is performed before the daily dose of thyroid hormone to obtain accurate measurements.

Normal TSH hormone values

TSH reference values may vary slightly between laboratories, and the physician will interpret the results considering different personal and clinical factors.

• Elevated TSH levels: They usually indicate hypothyroidism, with chronic thyroiditis (or Hashimoto's disease) being a common cause. Rarely, increased TSH may be due to problems in the pituitary gland, such as a tumour that increases its production, or inadequate medication control in patients undergoing thyroid treatment.
• Low TSH levels: They may be associated with hyperthyroidism or, to a lesser extent, with alterations in the pituitary gland that limit TSH production. It may also occur in patients under treatment with insufficient adjustment of their medication or during certain times of pregnancy.

Maintaining proper control of TSH levels allows for effective management of thyroid health and prevention of metabolic and energy-related complications in the body.

Reference values for TSH may vary slightly depending on the laboratory and method of analysis. However, in general terms, the TSH ranges for an adult are usually as follows:

• Normal TSH value: Between 0.4 and 4.0 mIU/L (thousand international units per litre).
• Elevated TSH (indicative of possible hypothyroidism): >4.5 mIU/L.
  • Subclinical hypothyroidism: TSH between 4.5 and 10 mIU/L, with T4 levels within normal range.
  • Clinical hypothyroidism: TSH >10 mIU/L, usually accompanied by low T4 levels.
• Low TSH (indicative of possible hyperthyroidism): <0.4 mIU/L.
  • Subclinical hyperthyroidism: TSH between 0.1 and 0.4 mIU/L, with normal T4 and T3 levels.
  • Clinical hyperthyroidism: TSH <0.1 mIU/L, with elevated T4 and/or T3 levels.

It is important to remember that these values may be adjusted depending on the patient's age, pregnancy status or specific conditions. For pregnant women, for example, TSH values tend to have lower limits, especially in the first trimester.

Other Considerations

1. Confirmation of diagnosisTSH: Although TSH regulates thyroid activity, TSH levels do not always fully reflect thyroid status. Measurement of T4 and T3 together with TSH helps to confirm the presence of hypothyroidism or hyperthyroidism and to assess its severity:
   • In the hypothyroidism, TSH is usually elevated, while T4 and T3 levels are low.
   • In the hyperthyroidism, TSH is usually low, with elevated T4 and T3 levels.
2. Detection of subclinical conditionsIn the hypothyroidism and the subclinical hyperthyroidism, TSH may be out of range while T4 and T3 remain normal. This test allows detection of these conditions early, facilitating close monitoring of thyroid function before clear symptoms become apparent.
3. Distinction of pituitary or thyroid causesIn cases of pituitary dysfunction, TSH levels may not adequately reflect thyroid function. Measurement of T4 and T3 is essential to determine whether the dysfunction is of thyroid origin or secondary to pituitary problems.
4. Assessment of T4 to T3 conversionT3: Most of the T3 comes from the conversion of T4. Measuring both hormones allows problems in this conversion to be identified, such as in central hypothyroidism or in some chronic diseases, where there may be normal levels of TSH and T4, but low T3, indicating a deficit in conversion.
5. Adjustment and monitoring of treatmentsIn patients under treatment for thyroid disorders, assessing TSH together with T4 and T3 allows for a more precise adjustment of medication doses, ensuring control of the disorder without inducing hormonal imbalances.

Bibliographical references 

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Alexander EK, Pearce EN, Brent GA, Brown RS, Chen H, Dosiou C, Grobman WA, Laurberg P, Lazarus JH, Mandel SJ, Peeters RP, Sullivan S. 2017 Guidelines of the American Thyroid Association for the Diagnosis and Management of Thyroid Disease During Pregnancy and the Postpartum. Thyroid. 2017 Mar;27(3):315-389. doi: 10.1089/thy.2016.0457. Erratum in: Thyroid. 2017 Sep;27(9):1212. doi: 10.1089/thy.2016.0457.correx. PMID: 28056690.

Chiovato L, Magri F, Carlé A. Hypothyroidism in Context: Where We've Been and Where We're Going. Adv Ther. 2019 Sep;36(Suppl 2):47-58. doi: 10.1007/s12325-019-01080-8. Epub 2019 Sep 4. PMID: 31485975; PMCID: PMC6822815.

Baumgartner C, da Costa BR, Collet TH, Feller M, Floriani C, Bauer DC, Cappola AR, Heckbert SR, Ceresini G, Gussekloo J, den Elzen WPJ, Peeters RP, Luben R, Völzke H, Dörr M, Walsh JP, Bremner A, Iacoviello M, Macfarlane P, Heeringa J, Stott DJ, Westendorp RGJ, Khaw KT, Magnani JW, Aujesky D, Rodondi N; Thyroid Studies Collaboration. Thyroid Function Within the Normal Range, Subclinical Hypothyroidism, and the Risk of Atrial Fibrillation. Circulation. 2017 Nov 28;136(22):2100-2116. doi: 10.1161/CIRCULATIONAHA.117.028753. Epub 2017 Oct 23. PMID: 29061566; PMCID: PMC5705446.