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Thyroid diseases are quite complex, their symptoms are inconsistent and very individual. This means that thyroid problems will look different for each person, sometimes for a long time the patient does not have any complaints.
In any case, it is important to have a general idea of how it works. In any case, it is important to have a general idea of how the thyroid gland works, why and what hormones it produces. This will help a person to detect the problem in time, take tests and ask the right questions to the doctor. Also, this data may provide clues about some of the mysterious symptoms that a person may experience in everyday life.
Key thyroid hormones are produced by the thyroid gland, an endocrine organ located in the lower, front part of the neck. Thyroid hormones enter the bloodstream and are carried to all body tissues. They help us use energy from incoming food, store and produce heat, stimulate the brain, heart, muscles and other organs.
The production of thyroid hormones is controlled by another endocrine organ, the pituitary gland, which is located in the brain. The pituitary gland secretes thyroid-stimulating hormone (TSH) into the blood to stimulate the peripherals. The amount of TSH that the pituitary gland sends into the bloodstream depends on the amount of peripheral thyroid hormones in the body. If the pituitary gland reads a low level of thyroid hormones, then it produces more of them. As soon as their level in the bloodstream rises above normal, the pituitary gland stops producing TSH. Thus, the pituitary gland senses and controls the synthesis of thyroid hormones.
What thyroid hormones should be donated
Hormone tests can show levels of total (protein-bound) and free hormones.
– The highest priority significant hormone is thyroid-stimulating hormone (TSH), – says endocrinologist Zukhra Pavlova. – It is synthesized in the brain and stimulates the thyroid gland, as well as the synthesis of the hormone thyroxine. Most often, doctors look at the amount of TSH, because this is the most indicative hormone – it reflects the lack of synthesis of thyroid hormones.
Most of the hormones in the blood bind to proteins – they help deliver them to organs and tissues. And only a small part of them is “free” to penetrate into tissues, directly exerting biological effects.
“The second priority is T4 free hormone, not associated with a carrier protein,” continues Dr. Pavlova.
T4 is the main form of thyroid hormone circulating in the blood (about 95% on average). To exert its effect, T4 is converted to T3 by removing an iodine atom. This occurs mainly in the liver and in certain tissues where T3 acts, such as the brain. T3 usually makes up about 5% of the thyroid hormones circulating in the blood.
“In diseases, doctors evaluate several factors,” says endocrinologist Zukhra Pavlova. – If there is a suspicion of an autoimmune thyroid disease, for example, an ultrasound doctor wrote in an ultrasound report that the patient has diffuse changes in the thyroid gland like thyroiditis, the doctor may prescribe tests for antibodies to the thyroid gland. If diffuse toxic goiter is suspected, tests for antibodies to thyroid-stimulating hormone receptors will be ordered. These tests will help to make the correct diagnosis and choose the appropriate treatment.
Analysis for TSH
The best way to initially check the activity of the thyroid gland is to measure the level of TSH. Changes in TSH can serve as a kind of early monitoring system. It often changes in advance, even before the actual level of thyroid hormones reaches low or too high levels.
High TSH is an indicator that the thyroid gland does not secrete enough T3 together with T4, which is possible with primary hypothyroidism. If TSH is low, this may indicate that the thyroid gland is too active, producing an excess of hormones, which is typical of hyperthyroidism.
Sometimes low TSH results from an abnormality in the pituitary gland that prevents it from producing enough hormone to stimulate the thyroid gland (central hypothyroidism).
T4 tests
The total T4 test measures plasma bound and free thyroxine (T4). Free T4 is not associated with protein molecules, it can freely penetrate into the tissues of the body and act on them. It is important to know that drugs and various pathological conditions affect the overall level of T4.
Estrogen, oral contraceptive pills, pregnancy, liver disease, or a viral infection (such as hepatitis C) are some of the common causes of an increase in thyroid hormone-binding proteins, leading to a high total T4 level.
Testosterone, androgens and anabolic steroids are common causes of a decrease in thyroid hormone binding proteins resulting in a decrease in total T4.
Sometimes, for example in pregnant women, there may be normal thyroid function, but the level of total T4 is outside the normal range. Blood tests that measure the free T4 index can more accurately reflect how the thyroid gland is functioning under these circumstances.
T3 tests
The T3 test measures the level of triiodothyronine (T3) in the blood. The total T3 test shows the bound and free fractions of triiodothyronine. Patients with hyperthyroidism usually have elevated total T3 levels. T3 tests can be used to confirm the diagnosis of hyperthyroidism and determine its severity.
In some thyroid disorders, T3:T4 ratios change and may provide diagnostic information. A significant increase in T3 relative to T4 is characteristic of Graves’ disease. Medications such as steroids and amiodarone, as well as severe illness, can reduce the amount of the hormone that the body converts from T4 to T3 (active form), leading to a lower proportion of T3.
T3 levels are the last to fall in hypothyroidism and therefore are not commonly used in diagnosing patient problems.
Functions of thyroid hormones
These hormones are essential for maintaining a healthy weight, energy levels, core temperature, skin, hair, nails, and many other functions.
The norm of thyroid hormones
| Normal TSH values | from 0,5 to 5,0 mIU/l |
| Normal values of free T4 | 0,7 to 1,9 ng/dl |
| Normal level of total T4 | from 5,0 to 12,0 μg/dL |
| Normal level of total T3 | 80 — 220 ng/dL |
The normal value of indicators is determined by measuring the hormone in a large population of healthy people and finding the normal (average) range of values.
What diseases are associated with thyroid hormones
Thyrotoxicosis. This condition often results from an overactive thyroid gland or hyperthyroidism and is associated with an increased amount of T3 in the bloodstream.
Signs of thyrotoxicosis include weight loss, increased appetite, increased heart rate, irregular menstrual cycles, fatigue, irritability, and thinning hair.
Hyperthyroidism. This is a condition in which the level of thyroid hormones is elevated. It occurs in conditions such as Graves’ disease, inflammation of the thyroid, or a benign tumor. Hyperthyroidism can also show up after taking T3 supplements.
Hypothyroidism. It occurs when the thyroid gland does not produce enough thyroid hormone. This may be due to autoimmune diseases such as Hashimoto’s thyroiditis or certain medications. Hypothyroidism can also occur when the pituitary gland is dysfunctional, such as pituitary tumors or inflammation. Hypothyroidism tends to run in the family and is more common in adults as well as women.
Symptoms may include fatigue, mental depression, feeling cold, weight gain, dry skin, constipation, and menstrual irregularities.
Where to get tested for thyroid hormones
Tests for the level of thyroid hormones are performed by both municipal laboratories and private centers. Analyzes can be either free, under the MHI policy, or paid, or under the VHI policy.
A doctor of any specialty can prescribe a study for thyroid hormones. The specialist will determine the indications for a consultation with an endocrinologist, or he will independently prescribe examinations, and if any deviations are found, he will refer him to an endocrinologist.
Popular questions and answers
We asked patients to answer typical questions about thyroid hormones endocrinologist Elena Zhuchkova.
Who needs to get tested for thyroid hormones and when?
• swelling or thickening in the neck;
• irregular, fast heart rate, or slow pulse;
• high cholesterol;
• osteoporosis, especially at a young age;
• alopecia, the appearance of dry skin, brittle nails, hair loss and brittleness;
• change in body temperature – a stable decrease or increase;
• problems with the onset of pregnancy or childbearing, menstrual irregularities;
• sleep disturbances – lack of sleep or constant drowsiness;
• chronic fatigue, persistent state of general weakness;
• increased appetite;
• pathologies of the thyroid gland in blood relatives;
• in children – with a delay in mental, sexual or physical development.
It is worth noting that changes in human behavior are also indications for the study of thyroid hormones: the appearance of lethargy, inactivity or, conversely, fussiness, irascibility, as well as progressive memory loss, a decrease in mood, apathy.
Today, thyroid hormone tests are included in the mandatory examination of a cardiologist, gynecologist, dermatologist, and some others.
As a rule, during the initial study, blood is donated for TSH, free T4, antibodies to TPO. Indications for a more advanced examination are determined by a specialist.
How do I prepare for a thyroid hormone test?
Blood for thyroid hormones can be taken in the morning, afternoon and evening, since their level practically does not fluctuate during the day. Women can be tested on any day of their menstrual cycle.
If you are taking thyroxine, do not cancel it in advance. Just skip the pill just before the test and don’t forget to take the drug after donating blood! Tell your doctor if you are taking any drugs (eg, corticosteroids, dobutamine, which may interfere with the result) and this will help you interpret the result correctly.