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FT3 and FT4 thyroid hormone tests can help you check if your thyroid is working properly. If the test result is abnormal – either below or above normal – this indicates either hypothyroidism or hyperthyroidism, which in turn may explain the appearance of various disturbing symptoms in the body, because if the thyroid is not working properly, the whole body will feel it.
FT4 – indications for testing the level of thyroid hormones
The main task of the thyroid gland is the production of three very important hormones for the entire body, such as:
- thyroxine — T4,
- trójjodotyronina — T3,
- and calcitonin.
The hormones T3 and T4 are called vital activity hormones due to the fact that they reach every living cell in our body. However, the level of the “steering” hormone produced by the pituitary gland is also very important. This hormone is thyrotropin, or TSH for short. If the level of these hormones in the body is disturbed, many different symptoms may appear, which indicate problems with the functioning of the thyroid gland.
The endocrinologist orders tests such as FT3 and FT4 or TSH. Even the family doctor, after observing the symptoms of a sick thyroid, may also order these tests. Symptoms of thyroid malfunction include goiter, dry and cool skin, drowsiness, excessive sweating, sudden weight gain and problems with losing weight, or even sudden weight loss or insomnia, and menstrual disorders. Interestingly, testing the level of thyroxine, or FT4, is also useful in the diagnosis of infertility in women (usually in the case of an abnormal TSH result).
Buy a test package on Medonet Market now. Thyroid function assessment – diagnostic tests and see if your thyroid is working properly.
In addition, in Poland, blood is collected in every newborn baby until the 5th day of life for screening for congenital hypothyroidism (a sample is taken from the heel of the newborn).
See also: Five things you need to know about hormones
FT4 – standards
The test is simply a blood sample taken from a vein in the arm and sent to a laboratory for analysis. Blood is collected on the so-called clot, i.e. with an activator that accelerates the blood clotting process. The test consists in proper preparation of the sample and then introducing it to the plate, where there are antibodies that form a complex with the FT4 hormone. In the next step, a substance which detects this complex, which emits light or produces a color combination, is added. The intensity of the color or the amount of light emitted is then measured. The greater the value, the greater the amount of test substance in the test tube.
You can order a home blood collection if you purchase the test package offered by uPatient’s company. At Medonet Market you will find a special package for people who plan to visit a dietitian. Pre-consultation tests with a dietitian – home blood analysis. One of the tests available in the package is the ft4 test.
You usually get your results on the second working day. Currently, the analysis of the result uses the determination of the free fraction of thyroxine, i.e. FT4, for which the standard is: 10-25 pmol / l (8-20 ng / l). With the level of TSH in the norm 0,4-4,0 uIU / ml.
Check it out: Hormones under control, i.e. the hormonal profile for women
FT4 – interpretation of results
It is very important to interpret FT4 and TSH together as both hormones work together in the body and are interdependent. A reduced FT4 level – below 10 pmol / l, and at the same time an increased level of TSH – above 4 uIU / ml, may indicate hypothyroidism, caused by insufficient amount of this hormone produced in the thyroid gland, or even iodine deficiency.
It may also indicate autoimmune diseases (e.g. Hashimoto’s disease), diseases of the pituitary gland or the presence of acute chronic diseases not related to the thyroid gland. This result may also appear in people treated with thyreostatic drugs.
On the other hand, an increased level of FT4 – above 25 pmol / l with a simultaneous reduced concentration of TSH – below 0,4 uIU / ml may indicate hyperthyroidism caused, for example, by Graves’ disease, hyperactive nodular goiter, early stages of Hashimoto’s disease, subacute thyroiditis or as a result of the treatment of hypothyroidism with thyroxine, iodine and heparin. It is worth mentioning that pregnancy can also affect FT4 levels.
Elevated FT4 levels (along with FT3) may also indicate postpartum thyroiditis or gestational thyrotoxicosis. However, these hormones do increase during pregnancy (especially in the second and third trimesters), and this is usually not an abnormality. Increased FT4 concentration may also occur when taking certain drugs, such as: hormonal contraceptives, preparations containing estrogens, antiepileptic drugs, large amounts of aspirin, agents used for contrasting. Increased levels may also be due to heroin use.
Find out more: What does the thyroid gland suffer from?
How to prepare for the FT4 test?
To avoid falsified results, it is best to test thyroid hormones such as FT3, FT4 or TSH on an empty stomach. If possible, you should refrain from taking medications that may interfere with laboratory determinations before the test and take them only afterwards.
FT4 testing should not be performed, for example, in patients who are on heparin therapy and for several days after stopping treatment.
The expert replies: What tests for the thyroid should be performed?
FT4 in pregnancy
During pregnancy, the metabolism of the thyroid gland increases (around week 16 of pregnancy by 10 percent, and by as much as 30 percent in the third trimester). Interestingly, according to the data, approximately 0,1 to 0,4 percent of pregnant women are hyperthyroidism, and 2,5 percent of pregnant women are hypothyroid. Keep in mind that Hypothyroidism increases the risk of pregnancy complications and adversely affects the development, especially intellectual, of the child.
However, it should be borne in mind that changes occurring in the pregnant body along with increased levels of hormone binding proteins, the concentration of FT4 and FT3 hormones may be naturally higher than in other people. Therefore, often different standards of FT4 concentration are used for pregnant women.
Find out more: Postpartum hormones – concentration, lactation, first menstruation
FT4 and the side effects of the test performed
In rare cases, complications may occur, such as:
- phlebitis;
- infection;
- excessive bleeding.
It is more common for people to feel pain or discomfort when taking blood. You may also experience light bleeding after removing the needle. A small bruise may appear around the puncture site.
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