The TSH test is used to assess thyroid function and is normally requested by the doctor when there is suspicion of changes in the thyroid, such as hypothyroidism or hyperthyroidism, for example.
TSH is a hormone produced by the pituitary gland in the brain and its function is to stimulate the thyroid to produce its hormones, triiodothyronine (T3) and tetraiodothyronine (T4). Therefore, when there is a change in the TSH test, normally the T3 and T4 tests may also be altered.
The result of the TSH test must be interpreted by the endocrinologist, together with other tests that assess thyroid function, and thus identify possible diseases and indicate the most appropriate treatment. See which tests are essential to evaluate the thyroid.
What is it for
The TSH test is indicated to assist in the diagnosis of:
- Primary, congenital, clinical or subclinical hypothyroidism;
- Clinical, subclinical or central hyperthyroidism;
- Graves’ disease;
- Tireoidite de Hashimoto;
- Thyroid cancer;
- Thyroid nodule or cyst;
- Tumor in the pituitary gland or pituitary adenoma.
In addition, the TSH test may also be requested to monitor the effectiveness of the treatment of thyroid diseases.
If you want to be monitored by an endocrinologist, make an appointment in the nearest region:
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When to take the exam
The TSH test is usually requested when symptoms appear that may indicate thyroid problems, such as weight change, goiter, dry skin, rapid heartbeat, tiredness or hand tremors. Check out the main symptoms of thyroid problems.
In addition to TSH, the doctor must order other tests that evaluate the thyroid, such as T3 and T4, measurement of antibodies such as anti-TRAB, anti-thyroglobulin and anti-TPO in the blood. In the case of suspected malignant lesions in the thyroid, the doctor may also request a biopsy, called Fine Needle Aspiration (FNA). Find out how the PAAF exam is carried out.
What is the function of TSH in the body?
The function of thyroid-stimulating hormone (TSH) is to stimulate the thyroid to produce its hormones, T3 and T4, which are responsible for maintaining the proper functioning of the heart, brain, liver, intestines and kidneys. In addition, thyroid hormones also regulate metabolism and body temperature and influence growth, menstrual cycle, fertility, weight and emotional state.
Therefore, when TSH values are increased in the blood, it means that the concentration of T3 and T4 in the blood is low. When found in low concentrations, T3 and T4 are present in high concentrations in the blood.
How to prepare for the exam
It is not necessary to fast to perform the TSH test, but some laboratories may recommend fasting for 4 hours, and it is important to consult the laboratory’s recommendations.
The best time to take this test is in the morning, as the concentration of TSH in the blood varies throughout the day. Furthermore, it is important to inform the doctor and the laboratory about the use of medications that may interfere with the results, such as lithium, amiodarone, potassium iodide, corticosteroids or biotin.
How is done
The TSH test is simple, carried out in the laboratory by taking a blood sample that is sent to the laboratory for analysis.
What is ultra sensitive TSH
The ultra-sensitive TSH test is a more advanced diagnostic method that can detect minimal amounts of TSH in the blood, which the normal test would not be able to identify. The diagnostic method used in laboratories is very sensitive and specific, with the ultra-sensitive TSH test normally used routinely.
TSH reference values
TSH reference values vary according to the person’s age and the laboratory in which the test is carried out, and are normally:
These values may vary depending on the laboratory, and therefore, the results must always be evaluated by the endocrinologist.
Reference values in pregnancy
During pregnancy, TSH reference values are different and are considered normal values:
Normally during pregnancy, the TSH hormone is lower and T4 may be elevated, due to thyroid stimulation by beta-HCG.
Therefore, the result of the TSH test must be interpreted by the obstetrician or endocrinologist, along with other tests that evaluate the thyroid.
How to understand the results
TSH results must be interpreted by the endocrinologist, along with other requested tests.
1. TSH alto
High TSH may indicate that the thyroid is producing less thyroid hormones or be related to some dysfunction of the pituitary gland in the brain.
The main conditions that can cause high TSH on examination are:
- Hypothyroidism: TSH may be high due to an attempt by the pituitary gland to stimulate the production of thyroid hormones, when they are low, and generally in this condition the TSH is high and the T4 is low. However, in subclinical hypothyroidism TSH is high, but T4 is within normal limits. Know what T4 is;
- Use of medicines: the use of low doses of medicines against hypothyroidism, such as levothyroxine, or other medicines, such as propranolol, furosemide, lithium and medicines with iodine, can increase the concentration of TSH in the blood;
- Pituitary tumor: it can also cause an increase in TSH.
Symptoms related to high TSH are typical of hypothyroidism, such as tiredness, weight gain, constipation, feeling cold, increased hair on the face, dry skin, brittle and brittle hair and nails. Know how to identify the symptoms of hypothyroidism.
2. Low TSH
Low TSH may indicate that the thyroid is producing more thyroid hormones or be related to changes in the pituitary gland.
The main conditions that can cause low TSH are:
- Hyperthyroidism: low TSH normally indicates that the thyroid is producing T3 and T4 excessively, and therefore the pituitary gland reduces the release of TSH to try to regulate thyroid function. Understand what T3 is;
- Medication use: When the dose of levothyroxine for hypothyroidism is too high, TSH values are below ideal. Other medications that can cause low TSH are: AAS, corticosteroids, dopaminergic agonists, fenclofenac, heparin, metformin, nifedipine or pyridoxine, for example.
- Pituitary tumor: it can also lead to low TSH.
Symptoms related to low TSH are typical of hyperthyroidism, such as agitation, heart palpitations, insomnia, weight loss, nervousness, tremors and decreased muscle mass.
In this case, it is normal for TSH to be low and T4 to be high, but if T4 is still between 01 and 04 μIU/mL, this may indicate subclinical hyperthyroidism.
Low TSH and low T4 may indicate anorexia nervosa, for example, but in any case the diagnosis is given by the doctor who requested the test. Learn more about the treatment of hyperthyroidism.
