Hormonal analysis in the diagnosis of thyroid diseases: A lecture

Abstract

The creation of methods of radioimmunological analysis (RIA) to determine hormones had a decisive influence on the development of modern endocrinology and especially thyroidology. Since 1973, RIA methods have become routine diagnostic methods for the determination of thyroxine (T4), triiodothyronine (T3) and thyroid stimulating hormone (TSH). However, for a long time they made it possible to determine only the fractions of hormones associated with transport proteins, and RIA methods for determining TSH did not allow to determine its low (< 0.1 Mme/l) concentrations. Later, variants of RIA were developed based on the immunometric principle, using solid-phase carriers and monoclonal antibodies. This made it possible to determine, along with the general T4 and T3, also their free forms. Namely free T4 and T3 (FT4 and FT3) provide the entire spectrum of biological activity. Their definition is the most informative in assessing the functional state of the hypothalamus-pituitary-thyroid gland. The IRMA principle allowed to increase the sensitivity of the method for determining TSH to 0.16 mIU/L. This level of sensitivity satisfied clinicians in assessing the euthyroid state and hypothyroidism, but it did not allow to differentiate the normal level of TSH from subnormal in patients with thyrotoxicosis. In the last decade, fundamentally new non-isotopic technologies of hormonal immunoassay have been created. The sensitivity of this method in determining TSH was brought to 0.03 mIU/L. Currently, the determination of FT4 and TSH using the hypersensitive method is a strategic diagnostic approach to assessing the hormonal status of the thyroid gland.