Description

The thyroid gland exerts powerful and essential regulatory influences on growth, differentiation, cellar metabolism and general hormonal balance, as well as on the maintenance of metabolic activity and the development of the sketeal and organ system.

T4 is the most commonly measured substance in the assessement of thyroid function. Most of the thyroxine secreted into the bloodstream is bound to a transport protein, thyroxine binding globulin (TBG), and to albumin and pre-albumin. Only less than 1% of thyroxine remains unbound as free T4 in blood. Elevated total thyroxine levels have been associated with hyperthyroidism, a condition with an excess amount of circulating thyroid hormone and decreased total thyroxine levels have been associated with hypothyroidism,a condition with insufficient levels of thyroxine concentration. Primary malfunction of the thyroid gland or any diseases affecting the thyroid-pituitary-hypothalamus system may result in the abnormal thyroxine concentration in blood. Measurement of thyroxine has been one of the most widely used method for evaluation of an individual’s thyroid status.