In line with its mission, the Editorial Board of MedTvoiLokony makes every effort to provide reliable medical content supported by the latest scientific knowledge. The additional flag “Checked Content” indicates that the article has been reviewed by or written directly by a physician. This two-step verification: a medical journalist and a doctor allows us to provide the highest quality content in line with current medical knowledge.
Our commitment in this area has been appreciated, among others, by by the Association of Journalists for Health, which awarded the Editorial Board of MedTvoiLokony with the honorary title of the Great Educator.
The FT3 test, i.e. the concentration of free triiodothyronine (T3) and the thyroxine (T4) test, are ordered when thyroid diseases are suspected. T3 and T4 are hormones produced by this gland, so by determining their level, you can check how the thyroid works and whether the body has developed inflammation, hypothyroidism or hyperthyroidism. The thyroid gland itself is a very important gland, because if it produces too little of the hormone, changes can occur in the central nervous system. Especially correct T3 and T4 levels are important for infants as a deficiency can cause mental retardation. Therefore, today all newborns are screened for congenital hypothyroidism. However, the thyroid gland may fail to function properly for a variety of reasons, and therefore, adults may develop a deficiency or excess of thyroid hormones.
Purpose of the FT3 study
FT3 and FT4 tests and the determination of TSH levels are performed in patients with suspected thyroid disease. The determination of the free fractions of the thyroid hormone and TSH allows for an objective determination whether the thyroid gland is functioning properly, or whether it has become overactive or underactive. However, it is important to inform your doctor about any medications you are taking before the test, as the levels of T3 hormone may be affected by estrogens, antiepileptic drugs or contraceptives, although they should not affect the FT3 test result. In addition, in some people, FT3 testing is only performed when TSH levels are above normal.
Course of the FT3 study
The T3 hormone – triiodothyronine accounts for only 10 percent of all thyroid hormones, although it is responsible for most of its actions and is 3-4 times more powerful than the T4 hormone. The T3 hormone is bound in the blood serum in 99,7%. with proteins, and the rest is free. Therefore, in the course of the FT3 test, the level of T3 unbound with proteins is determined.
For testing, a blood sample is taken from a vein in the arm and an immunological test is performed on the sample.
In the test package Pre-consultation with a dietitian – home blood analysis available on Medonet Market, you can purchase an option with blood sampling at the patient’s home. Such a package of tests will allow to determine the parameters checking, among others deficiencies and the presence of inflammation.
The T3 hormone binds to its specific antibodies on the platelets, so it can be separated from other compounds in the blood sample. The substance which detects the hormone triiodothyronine, which is most often an antibody, is then introduced into the sample. Such a compound emits light, the intensity and color of which are measured to determine the amount of FT3 on the wafer.
Interpretation of FT3 results
The FT3 norm ranges from 2,25 to 6,0 pmol / L (1,5–4,0 ng / L), with the TSH normal being 0,4–4,0 µLU / ml. In order to read the FT3 result, it is necessary to associate it with the TSH result. Thus, if FT3 is elevated above 6 pmol / L, and TSH is below 0,4 µLU / ml, the thyroid gland is hypothyroid.
On the other hand, an FT3 result below 2,25 pmol / L and an elevated TSH result above 4,0 µlU / ml may indicate hyperthyroidism.
It is worth knowing that the FT3 level test is performed in the diagnosis of hyperthyroidism, because the pathological T3 hormone increases earlier than the T4 hormone, but also returns to the normal norm later. Therefore, this test can detect hyperthyroidism, and in the case of hypothyroidism, the determination of TSH alone is usually sufficient.
| Name of the study | FT3 |
| Introduction – what is this research / what the research is for | The FT3 test, i.e. testing the concentration of free triiodothyronine (T3) and testing the level of free thyroxine (T4), is ordered when thyroid diseases are suspected. T3 and T4 are hormones produced by this gland, so by determining their level, you can check how the thyroid functions and whether the body has developed inflammation, hypothyroidism or hyperthyroidism. The thyroid gland itself is a very important gland, because if it produces too little of the hormone, changes in the central nervous system can occur. Especially correct T3 and T4 levels are important for infants as a deficiency can cause mental retardation. Therefore, today all newborns are screened for congenital hypothyroidism. However, the thyroid gland may fail to function properly for a variety of reasons, and therefore adults may develop a deficiency or excess of thyroid hormones. |
| Indications for the examination | Diagnosis of thyroid disease |
| Standards | 2,25–6 pmol / L (1,5 – 4 ng / L) with normal TSH level 0,4 – 4,0 µIU / ml |
| Interpreting the results (at least basic) | Increased FT3 (ie over 6 pmol / L, ie 4 ng / L) with simultaneous reduction of TSH level below 0,4 µIU / ml may indicate hyperthyroidism. However, an FT3 result below 2,25 pmol / L, ie 1,5 ng / L with a TSH level above 4,0 µIU / ml, indicates hypothyroidism. |
| How is the test going | For testing, a blood sample is taken from a vein in the arm and an immunological test is performed on the sample. |
| Information to be reported prior to testing | Medications taken |