Assessment of the functional activity of the parathyroid glands is frequently required in clinical medicine for the evaluation of abnormalities of mineral metabolism. The interpretation of determinations of parathyroid hormone (PTH) by radioimmunoassay is complicated by the fact that several species of immunoreactive PTH exist in the circulation as a consequence of metabolism of PTH in peripheral tissues as well as the secretion of PTH fragments from the parathyroid glands. Antisera to PTH may be directed towards limited regions of the PTH molecule. In general, antisera may be considered in three groups: those with antigenic determinants directed only towards the amino-terminal region of intact PTH (N-terminal assay), those with antigenic determinants only for the carboxy-terminal region (C-terminal assays) and antisera with determinants for several sites within the PTH molecule (polyvalent assays). Although the structural requirements for biological activity reside within the amino terminal 34 amino acids of intact PTH, experience has shown that PTH immunoassays directed towards this portion of the PTH molecule have limited clinical value. Paradoxically, assays directed towards the biuologically inactive carboxy-terminal region of PTH which detect intact PTH and carboxy-terminal fragments, have been shown to be most useful in the clinical setting. An understanding of the metabolism of PTH, the fate of the hormonal fragments, and the immunological characteristics of the assay are essential for the application and interpretation of determinations of immunoreactive PTH in the clinical setting.
|Number of pages||8|
|Journal||Mineral and Electrolyte Metabolism|
|State||Published - Jan 1 1980|