Abnormal T3 and T4 levels may be a sign of a serious hormonal imbalance. Thyroxine, or more simply T4, is one of the hormones produced by the thyroid gland which contains four iodine molecules. It was first synthesized in 1927 by British chemists, Harington and Barger. Through a process of deionidation of T4, the follicular cells of the thyroid gland produce another hormone, called T3. T4 is a prohormone for T3 and it is produced in a larger quantity than T3. The phenyl portions of tyrosine residues from a peptide (thyroglobulin) are iodinated and covalent bonded process from which results thyroxine. The production of both T3 and T4 are activated by the thyroid stimulating hormone or the TSH. Actually, after the deiodination of T4 in the thyroid, thyroxine is converted to T3, hormone which will inhibit THS. T4 plays an important role in controlling the rate of metabolic processes that occur in the body, and it also influences physical development. Most of the T4 hormone that is transported in blood is protein bound, transthyretin and serum albumin. The half-life of T4 in the blood is approximately 1 week.
The main diseases related to the abnormalities of this hormones levels are hyperthyroidism and hypothyroidism. The thyroid laboratory tests may reveal elevated or decreased levels of T4. In the first case, the patient is suspected of hyperthyroidism and in the second, of hypothyroidism. However, the laboratory tests may not be conclusive since any change in the protein levels will affect total T4 levels because T4 is bound to proteins. This does not mean that the level of T4 is truly modified. The results may also be misleading with patients who take estrogen as a part of a hormone replacement therapy, those who take birth control pills and it can also be a result of pregnancy. Hyperthyroidism symptoms include weight loss, anxiety, hair loss, muscle pain, weakness, sometimes depression, polyuria or delirium. Untreated hyperthyroidism may lead to osteoporosis. In some cases, both thyroidal diseases may have no symptoms at all.
The normal T4 and T3 levels are 100 to 200 ng/dL for T3 and 4.8 to 10.4 mcg/dl for T4 in adults. However, a higher level of T4 is considered to be normal in pregnancy because of the changes in protein levels. There are free T3 and T4 tests and total T3 and T4 tests. Thyroid related conditions may easily be revealed with simple blood tests or with specific hormonal tests. It is recommended that the laboratory tests will also include a THS test and after comparing all the results the endocrinologist can establish a conclusive diagnosis. It is also recommended that the tests will be repeated for several times to obtain a more conclusive result.
Maintaining T3 and T4 levels normal is important for the body, since this hormones have an impact on mostly all the tissues in the body and any abnormality of these levels should be checked taken care of so complications could be avoided.