TSH (Hormone)

TSH (thyroid stimulating hormone) level refers to the concentration of the hormone that regulates thyroid hormones (T3, T4). TSH also has a stimulating effect on the growth, iodine uptake and thyroid hormone production of the thyroid gland. TSH production is primarily regulated by the pituitary gland and the hypothalamus. Thyrotropin-releasing hormone (TRH) stimulates the anterior pituitary lobe (HVL) to secrete TSH. Synonyms

• Thyroid-stimulating hormone (TSH).
• Thyrotropic hormone
• Thyrotropin
• TSHB (TSH, basal; TSH basal level).

Material needed

• Blood serum
• Or plasma (NH, LiH, K-EDTA)

Confounding factors

The following medications lower TSH levels:

• Heparin – blood thinning medication.
• Hormones
  • Dopamine and dopamine agonists: L-dopa, apomorphine, bromocriptine, lisuride.
  • Glucocorticoids
  • Catecholamines
  • Levothyroxine (thyroid hormone, T4)
  • Somatostatin (antagonist of growth hormone (synonyms: somatotropic hormone (STH), somatotropin), octreotide (a somatostatin analog).
• Morphine – strong analgesic
• Serotonin antagonists such as dolasetron – drugs used to treat nausea and vomiting, among other things.

The following medications increase TSH levels:

• Carbamazepine – drug used to treat mental illness.
• Hormones
  • Clomiphene – antiestrogen (to induce ovulation/ovulation).
  • Dopamine antagonists (see the list of hyperprolactinemia-inducing drugs under Laboratory Diagnostics under the topic Hormone Diagnostics “Prolactin” or “Hyperprolactinemia Due to Drugs“).
• Iodine in high doses
• Lithium – drug used for the treatment of mental illnesses
• Theophylline – medication used to treat chronic lung diseases such as bronchial asthma or chronic bronchitis

For these reasons, the affected person should appear for blood sampling in the morning before taking the medication (see also further notes below).

Normal values for TSH

Adult	0.27-4.2 μlU/ml [= mU/l]
Pregnant women (upper reference range)	1st trimester (third trimester): <2.5 2nd trimester: < 3.0 3rd trimester: < 3.5
Children up to the age of 17	0.27-5.0 μlU/ml
Infants (1st week to 1st year of life).	0.27-7.0 μlU/ml
Neonates (up to 1 week of life).	0.27-20 μlU/ml

Normal TSH values exclude manifest hypo- and hyperthyroidism.

Indications (areas of application)

• TSH level is determined when various thyroid diseases are suspected or for monitoring the progress of therapy.

Interpretation

	Primary hypothyroidism	Secondary hypothyroidism	Primary hyperthyroidism	Secondary hyperthyroidism
TSH	↑	↓/normal	↓	↑/normal
fT3, fT4	↓	↓	↑	↑

TSH values increased

• Primary hypothyroidism (fT4, fT3 also decreased).
• Secondary hyperthyroidism (fT4 simultaneously increased) – due to disorders of the pituitary gland.
• TSH-producing tumor (rare!).
• Genetic: TSH receptor mutations.
• Resistance to thyroid hormones (rare!).
• Partial organ damage due tocondition after radiotherapy, non-ablative radioiodine therapy, partial thyroidectomy (thyroidectomy).
• Medication (mentioned above).

TSH levels decreased

• Primary hyperthyroidism (fT4, fT3 borderline high or elevated).
• Secondary hypothyroidism (fT4, fT3 decreased) – usually due to global HVL insufficiency.
• Conversion increase intrahypophyseal: NTI = Non Thyroid Illness: simultaneously low fT3 (= conversion inhibition peripheral).
• Compared to nonsmokers, smokers have lower TSH levels on average, smoking women are more likely to have hyperthyroidism
• Medications (mentioned above)

Additional notes.

• Circadian fluctuations of TSH of 30% are considered quite “normal”.
• Some endocrinologists recommend as TSH standard range for adults: 0.27-2.50 µIU/ml. Notice. A lower TSH upper limit did not show a higher risk of coronary heart disease (CHD) or CHD-related death in a meta-analysis for adults at TSH levels between 3.5 and 4.5 mU/l than at levels between 0.5 and 1.5 mU/l.
• TSH secretion (TSH release) occurs in a pulsatile pattern, i.e., there is no steady release but rather a burst-like release with circadian rhythms (i.e., release that fluctuates throughout the day). The highest TSH values are measured early in the morning between 4:00-7:00 am. A value measured once is therefore always only a snapshot of limited significance.
• Thyroid and pregnancy: the European Thyroid Association (ETA; European Thyroid Association) has advocated universal thyroid screening of all pregnant women in for the first time.
  • The ETA Recommends TSH screening for all pregnant women at a minimum, including determination of thyroperoxidase antibodies (TPO-Ak) if necessary.
  • For normal thyroid function, an expectant mother needs about 50% more thyroid hormones in the early phase of pregnancy. Therefore, contrary to general recommendations, the TSH value should be determined in the pregnant woman already about the sixth week of pregnancy (SSW).
  • In pregnancy can be detected:
    • Normal: As a result of accelerated thyroid metabolism, there may be a nonpathological increase in triiodothyronine (T3) and thyroxine (T4). The concentration of thyroid-stimulating hormone (TSH), on the other hand, is often reduced in pregnant women. Due to the fact that the alpha chain of HCG is identical to the alpha chain of LH, FSH, and TSH, it can be explained that HCG has a thyrotropic effect (i.e. on the pituitary-thyroid control circuit). Therefore, in the 1st trimester (third trimester) of pregnancy, physiologically, there is an increased synthesis of T4 with the consequence that the endogenous TSH level is somewhat suppressed. This thyroid function normalizes no later than the second trimester.
    • Latent hypothyroidism (refers to a “mild” hypothyroidism), which is usually manifested only by a change in the thyroid parameter TSH: TSH > 4 mU / l, with concomitant normal T3 and T4 levels) – prevalence (disease frequency) about 10% (of pregnant women).
    • Latent hyperthyroidism (refers to a “mild” hyperthyroidism), which is usually manifested only by a change in the thyroid parameter TSH. The TSH value < 0.3 mU/l, with normal free T4 at the same time) – prevalence about 4%.
    • Manifest hypothyroidism – prevalence about 0.4 %.
    • Manifest hyperthyroidism – prevalence 0.1 to 0.4%.
  • Pregnancy – TSH findings and further procedure:
    • TSH > 4 mU/l → determination of fT4, TPO antibodies and thyroid sonography.
    • TSH < 0.3 mU/l → determination of fT4, FT3 and test for TSH receptor antibodies (TRAK) and thyroid sonography.
• Patients with manifest hypothyroidism: when therapy with L-thyroxine (T4) reveals euthyroidism with TSH levels in the reference range, patients show significantly higher LDL and triglyceride levels than matched control subjects despite apparently sufficient LT4 administration. CONCLUSION: The apparent euthyroid metabolic situation (normal metabolic situation) did not normalize these targets of thyroid hormones in the formerly hypothyroid patients.