TSH is a protein secreted by the pituitary gland that controls the secretion of thyroid hormones. The blood TSH level test is an important parameter for the assessment of thyroid function due to its high sensitivity. How to prepare for the TSH test? What does too low or too high TSH level mean?

Thyroid tests

Thyrotropin , abbreviatedTSHis a hormone produced by the anterior pituitary gland. This hormone stimulates the production of triiodothyronine (T3) and thyroxine (T4) by the thyroid gland. An increase in T3 and T4 inhibits the secretion of TSH, and a decrease in T3 and T4 stimulates the secretion of TSH. In addition, TSH secretion itself is regulated by thyreoliberin (TRH) produced in theof the hypothalamus .

TSH levels change even with slight fluctuations in blood T3 and T4 levels, therefore TSH is ascreening testin the assessmentthyroid function. Currently, the determination of TSH is the most sensitive methodto assess the deficiency and excess of thyroid hormones .

Sensitivity is over 95% and specificity is around 90%. In case of incorrect TSH concentration, the level of free T3 and T4 hormones should be determined.

TSH test - indications

The indication for TSH testing is suspected hyperthyroidism, which may be manifested by:

  • chronic fatigue,
  • easy fatigue,
  • excessive sleepiness,
  • constipation,
  • increased body weight,
  • hoarseness,
  • depressed mood,
  • problems with memory and concentration,
  • dry skin,
  • brittleness of hair and nails.

The indication for TSH testing is also suspected hypothyroidism, which may be manifested by:

  • over-stimulation and mobility,
  • frequent diarrhea,
  • losing weight,
  • shaking hands,
  • insomnia,
  • with increased sweating,
  • palpitations,
  • feeling hot.

Other indications for a TSH test are:

  • monitoring the effectiveness of treatment in hypothyroidism and hyperthyroidism,
  • neonatal screening for hypothyroidism - this test is of great importance in detecting congenital hypothyroidism, as it istreatment prevents mental retardation and growth retardation,
  • diagnosis of infertility in women,
  • diagnostics of thyroid diseases in pregnant women.

TSH test - what is the test and how to prepare?

To perform the TSH test, you will needvenous blood taken from the elbow bend . Blood is collected on the so-calledclot , i.e. with aactivator accelerating the blood clotting process . Although the daily fluctuations in TSH levels are small and are of no importance in routine diagnostics, theTSH test should be performed on an empty stomach , preferably between6: 30 and 9: 00 .

The collected blood is then transported to the laboratory, where TSH should be determined using the so-called3rd and 4th generation testsbased on enzymatic (eg ELISA) and chemiluminescent methods (eg CLIA). The use of 3rd and 4th generation tests guarantees the appropriatesensitivity of TSH determinations.

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TSH test - laboratory standards

The scope of the norm for TSHdepends on variousfactors , e.g.agesandtrimester of pregnancy . In addition, the level of TSH is influenced by the supply of iodine, as well as the methods used for determinations in individual laboratories. Usuallythe norm on the TSH test results is in the range 0.2-5 mIU / l . Therefore, always compare your result with the standard that is given onof the test result printoutand contact your doctor.

For children, the norms for TSH are slightly different and they are:

  • newborn: 1.3-19 mIU / l
  • child of 10 weeks: 0.6-10 mIU / l
  • child of 14 months: 0.4-7 mIU / l
  • child of 5 years: 0.4-6 mIU / l
  • child of 14 years: 0.3-5 mIU / l

Also upregnantnorms for TSH are different than for other people. According to the European Thyroid Society (ETA), the upper norm values ​​for TSH in each trimester should be 2.5 mIU / L forof the first trimester, 3.0 mIU / L for the second trimester and 3.5 for the third trimester. mIU / l . However, in the recommendations of the Polish Endocrinology Society of 2011, only one value is given, regardless ofpregnancy period - 2.5 mIU / l.

There is also an emphasis on setting norms locally for TSH. For the Polish population, according to the research from 2022, the norms for pregnant women are as follows:

  • pregnant in the first trimester: 0.009-3.18 mIU / l
  • pregnant in the second trimester: 0.05-3.44 mIU / l
  • pregnant in the third trimester: 0.11-3.52 mIU / l

It is worth noting that the lowest normal TSH concentration is observed in the first trimester of pregnancy, which results from the highconcentration of human chorionic gonadotropin (hCG)taking overstimulating function TSH .

TSH study - controversy

The norm for TSH is quite broad, which is due to the fact that the pituitary gland regulates TSH secretion in response to T3 and T4 varies individually in the population. For this reason, some clinicians believe that the upper limit of normal for TSH should be lowered.

It is postulated that this should be reduced to2.5 or 3 mIU / L , which could aid in the diagnosis of subclinical hypothyroidism (with normal T3 and T4 levels). Many studies have shown that in somehe althy, pregnant and elderly people , despite elevated TSH levels, thyroid hormones are normal.

It has also been documented that people with TSH values ​​close toupper normmay have more abnormal lipid profile parameters, high blood pressure,high body mass index and a higher risk of developing metabolic syndrome and cardiovascular diseases, compared to people with TSH values ​​inlower normal limits .

Nevertheless, this issue requires further research, as there are currently no large controlled clinical trials confirming the benefits of treatment in people with normal TSH values.

TSH test - what does too low or too high TSH level mean?

Too low TSH level in the blood may be due to:

  • primary hyperthyroidism,
  • Graves' disease,
  • administering thyroid hormones,
  • pituitary damage e.g. trauma, cancer, necrosis, inflammation.

Excessive TSH levels in the blood may be due to:

  • primary hypothyroidism,
  • Hashimoto's diseases,
  • pituitary adenoma,
  • neoplastic tissue outside the pituitary gland.

It is important to know thathyperthyroidism and hypothyroidism may be subclinical . Then the TSH is abnormal (too low or too high) and the levels of free T3 and T4 are normal.

TSH test - antibodiesTRAb

Wdiagnostics of thyroid diseasesit is useful toassess the presence of anti-TSH receptor antibodies in the blood (TRAb) . TRAb antibodies allow for the differential diagnosis of autoimmune thyroid diseases (e.g. Graves' disease) and other types of thyroiditis.

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