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Endocrinology studies the elaboration, secretion, transportation, and action of hormones at the clinical, cellular, and molecular levels. Hormones regulate bodily functions over relatively large distances using the bloodstream or over short distances on a cell-to-cell basis. The clinical effects of hormonal dysfunction can be classified broadly into hormonal excess or deficiency. Endocrine testing utilizes the principle that suppression tests test for hormone excess, whereas stimulation tests identify hormone deficiency. These tests are conducted on the background of varying factors that modulate hormonal secretion, so results need to be cautiously interpreted. Probability theory is helpful in this situation by increasing or decreasing the likelihood of disease presence.

Publisher Summary This chapter reviews the theoretical and technical aspects of radioimmunoassay (RIA) with particular emphasis on the interrelationships between the complications introduced into RIA by the heterogeneity of the peptide hormones and the new insights produced thereby into the related biosynthetic and degradative processes. The approach has been quite general in its concern with problems and pitfalls common to all assays, whether those in which the reagents are prepared in a research laboratory or those in which commercial sources supply the separate reagents or complete kits. For the latter, there is an additional complication, namely that of quality control of the kits. There are at least two aspects to this problem: quality control by the manufacturer at the time of preparation and the subsequent alterations introduced by handling and mishandling particularly when clinical samples are assayed. For the diagnosis of states of hormonal excess or deficiency the problem is often best solved by clinical rather than chemical control, e.g., by the use of appropriate stimulation or suppression tests, so that the accuracy of the absolute hormonal level is of less significance. For the other substances now measured by RIA, no one has yet provided a uniquely satisfactory answer to the general problem of quality control.