What is high and low TSH, reference values ​​and examination


What is TSH?

TSH is a hormone produced in the pituitary gland, which stimulates the thyroid gland to produce two hormones, triiodothyronine (T3) and thyroxine (T4), responsible for regulating metabolism by transforming nutrients into energy.

The pituitary gland is a gland located in the lower part of the brain that, among other things, has the function of regulating the activity of other glands, such as that of the thyroid. In a healthy individual, this gland releases TSH, which stands for Thyroid Stimulating Hormone Thyroid Stimulating Hormone -, based on thyroid hormone levels, to prevent it from producing insufficient or excess hormones.

If T3 and T4 levels are below normal in the bloodstream, metabolism slows down and TSH levels rise to stimulate hormones. Otherwise, that is, if the levels of T3 and T4 are very high, the metabolism accelerates and the pituitary gland reduces the release of TSH, to decrease the stimulus under the thyroid.

If these hormones are not produced correctly, it can, in severe cases, lead to mental illness in young children, difficulty in growth and development of school-age children and other illnesses in adults.

What is the TSH test for

The TSH exam is requested by the general practitioner or endocrinologist to assess the proper functioning of the thyroid. The procedure is performed together with other laboratory tests that measure the levels of free T3 and T4 and that determine the diagnosis of excess or insufficiency of hormones in the bloodstream.

Even if there is no family history of illnesses or symptoms, thyroid monitoring should start at age 40, if it has not been started before.

The main alterations of the thyroid gland are hypo and hyperthyroidism . The hypothyroidism is caused by a lack of thyroid hormones and TSH excess. When TSH is high, the patient’s thyroid functions slowly due to the lack of metabolism hormones, which can cause weight gain due to fluid accumulation. Hyperthyroidism is caused by excess hormones and shortages of TSH.

When TSH is low, metabolism accelerates with stimuli and the thyroid works more than it should, which makes the fat and calorie burning process more efficient. However, cases of low TSH can lead to abrupt and unintended weight loss and decreased muscle mass rate.

Typically, what leads to ordering the exams are the following reasons:

  • Patient with symptoms of hypothyroidism: tiredness, weight gain, discouragement, weak nails, slow speech, cold, memory loss, increased hair and acne.
  • Patient with symptoms of hyperthyroidism: heart palpitations, weight loss, feeling of heat, damp skin, insomnia, diarrhea, nervousness, tremors.
  • Monitor treatments for hypo and hyperthyroidism: to assess whether TSH levels are controlled and whether dose adjustment is necessary, new tests are performed every 6 to 8 weeks.
  • Pregnancy: if you are pregnant or planning to become pregnant. The test helps to diagnose infertility problems in women.

The TSH exam can show that the thyroid is in its normal functions and, in these cases, the problem is in the pituitary gland and the difficulty in producing the TSH.

In addition to the change in the level of hormonal production, the increase in thyroid growth and the formation of nodules, benign or malignant, can also be previously recognized through this test. However, other methods must be used to make a concrete diagnosis.


The examination is quick, simple and, generally, only a 3-hour fast is necessary. There are no other specific preparations for counting TSH, however, the patient must inform the doctor about the consumption of medications for continuous use.

Under the supervision of professionals, it is helped to pause the use of some medications for a period of time to avoid affecting the results of the exams, such as:

  • Amiodarone ;
  • Dopamine ;
  • Lithium ;
  • Potassium iodide ;
  • Prednisone or other glucocorticoid medications.

Tests involving radiation, such as x-rays , and cases of high stress can also alter the results. Other variations in thyroid hormones can be caused by:

  • Pregnancy;
  • Liver diseases;
  • Systemic diseases;
  • Estrogen.

How the TSH test is done

The TSH test is performed by collecting blood in a hospital or clinical analysis laboratory. The blood is placed in packaging tubes and taken for analysis, which usually delivers the results within 2 to 3 days.

TSH values ​​may vary during the day, so it is advisable to get tested early in the morning. After the exam, the patient can eat normally.

Exam results

The ultra sensitive TSH test is the new model used for this test, named in this way because it has the ability to detect levels as low as TSH as 0.1 mU / L (milliunits (mU) per liter of blood (L)).

The reference values ​​of the exam may vary from one laboratory to another, but, in general, it has the similarity of the following results:

TSH levels for newborns

  • Premature children (between 28 and 36 weeks): 0.7‑27 mIU / L.
  • Newborns (between 1 to 4 days) : 1 to 39 mU / L.

TSH levels for children and adolescents

  • Between 2 and 20 weeks: 1.7‑9.1 mIU / L.
  • Between 21 weeks and 20 years: 0.7 to 6.4 mU / L.

TSH levels for adults

  • Between 21 and 54 years: 0.4 to 4.5 mU / L.
  • Between 55 and 87 years : 0.5‑8.9 mIU / L.

TSH levels during pregnancy

  • First semester : 0.3‑4.5 mIU / L.
  • Second semester : 0.3‑4.6 mIU / L.
  • Third semester: 0.8‑5.2 mIU / L.

The results may demonstrate TSH above or below the ideal level for your age. These values ​​are caused by different conditions:

High TSH

  • Hypothyroidism: TSH levels rise to stimulate the thyroid, which is producing insufficient T3 and T4 hormones for the body’s metabolism. Hashimoto’s thyroiditis is the most common cause of primary hypothyroidism.
  • Pituitary tumor: Although rare and uncommon, a tumor in the pituitary gland can increase TSH production.
  • Medications for hypothyroidism: if the patient does not make the correct use of medications for hypothyroidism, TSH levels will rise again.

High TSH in infants and children

Thyroid dysfunction can happen at any age and for similar reasons, but high TSH levels in children are more severe than in adults. Symptoms include slow growth, muscle weakness, rare and hard stools, dry skin and obesity , even without large food intake.

The main reason that the TSH level rises in children is hypothyroidism. The TSH exam is performed at the maternity hospital, to ensure the health of the newborn, especially if the mother has the disease. Thyroid hormone plays an important role in maintaining a healthy pregnancy, so children born to mothers with hypothyroidism not properly treated may have congenital hypothyroidism, a hereditary disease that makes it impossible for the thyroid gland to generate the T4 hormone.

Having the disease right at birth causes developmental problems and, in severe cases, can lead to mental retardation and heart failure.


  • Hyperthyroidism: the excess production of hormones T3 and T4 generates a shortage of TSH. Hyperthyroidism can be caused by Graves’ disease, a toxic multinodular goiter or a benign tumor called a toxic nodule.
  • Pituitary damage: called secondary hypothyroidism, the pituitary gland is unable to produce the correct TSH values ​​by the thyroid gland.
  • Medicines for hypothyroidism: the drugs indicated for hypothyroidism reduce TSH levels in the bloodstream, however, overdoing their doses leads to lower than normal TSH values.
  • Pregnancy: the TSH production interval is different in the body while the woman is pregnant, especially in the first trimester. Your doctor may suggest that you take medications to stimulate thyroid hormones, even if your TSH is normal.

Low TSH in infants and children

Low TSH in children can also have causes similar to those in adults. Symptoms include extreme nervousness, hyperactivity, swelling at the base of the neck, hoarse voice and extreme thinness, even with a healthy appetite.

The main reason that TSH causes children to get low is hyperthyroidism, which can be caused by thyroiditis , thyroid inflammation, or a low iodine diet. Congenital hyperthyroidism is a rare condition, but it can be transferred by the mother to the fetus during pregnancy. Unlike maternal hypothyroidism, there is no evidence that it causes mental retardation in newborns.


At the time of the examination, the needle stick is described as mild, short-lived pain. However, the veins and arteries vary with each patient, so taking a blood sample can cause some complications for some, including:

  • Excessive bleeding, especially for people with bleeding disorders. If you have problems with bleeding or clotting, inform your doctor before taking a blood sample;
  • Fainting or feeling dizzy;
  • Bruises, which can be reduced by pressing the injection site for a few minutes;
  • Infection;
  • In rare cases, the vein may become swollen after the blood sample is taken. This problem is called phlebitis and can be resolved with a hot compress a few times a day.

TSH exam prices

The TSH exam can be performed by public or private network, under the standard name of TSH and free T4. In the second case, the amount may vary according to the region where the exam will be performed. On average, the price varies between R $ 30 and R $ 50 in popular laboratories, and up to R $ 90 in other clinics.

The TSH test is responsible for diagnosing several diseases that involve the thyroid gland. As stated throughout the article, it is a simple procedure that can be added as one of the routine tests to keep your body protected and monitored.

Share this text with your friends and family to inform them about the exam and visit your doctor to ensure more enlightening results.