Cortisol is the major glucocorticoid secreted by the adrenal cortex. Ninety percent of glucocorticoids is cortisol, 10% is corticosterone and very small in amount of 11-deoxycoritsol.
Cortisol assays are widely used in conjunction with diurnal measurements, ACTH and dexamethasone, suppression for the diagnosis of Addison´s disease, Cushing´s disease, and malfunction of hypothalamus or pituitary.
A variety of assay techniques were devised for the determination of plasma cortisol i.e., colorimetry by Silber et al. in 1954, fluorometry by Sweat et al: in 1952 and by Matlingley et al. in 1962, Competitive proteins binding assay (CPB) by Murphy et al. in 1963, radioimmunoassay (RIA) by Ruder et al. in 1972, and enzymeimmunoassay (EIA) by Dray et al. in 1975.
Since the early 1970´s RIA method has been increasingly employed, senstitivity and specificity being increased more and more.
RIA method, however, has the following disadvantages.
1. Stricter rules and regulations for the preparation, transport, use and disposal of radioactive isotopes leading to high costs.
2. Equipment, laboratory facilities and technologist to meet high standards for RIA work, again leading to higher costs.
3. Increased desire to perform their own assays in the hospitals with limited laboratory facilities.
4. The limited shelf life of the label.
Although EIA is still in early phase of development, it is considered to have. the possibility of becoming a more specific and sensitive assay and to replace the well established RIA in the future. In Korea some laboratories began to employ EIA method since 1981. Now our laboratory has been using ELISA method for the diagnosis of Rota virus infection as well as electromicroscopy study.
Serum cortisol levels of non-selective healthy 80 men were measured by RIA and EIA method using Gamma Coat 1251 cortisol radioimmunoassay kit and ENDAB cortisol enzymeimmunoassay kit, respectively. Blood was taken between 9 to 11 o´clock in the morning, the results are as follows
1. The values of serum cortisol determined by methods of both RIA and EIA were 9.73 ±3.96 ug%, 8.06±3.17 ug%, respectively.
2. EIA method was well correlated with RIA method (r=0.92).
3. The coefficient of variation in EIA method was 7.9%.
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