Until recently, the measurement of circulating parathyroid hormone (PTH) has been unsatisfactory due to poor analytical performance of immunological assays and due to interference in such assays by circulating biologically inactive fragments of PTH. The development of a two-site immunometric assay with the use of acridinium ester as label has solved these problems. This immunochemiluminometric assay (ICMA) measures the intact molecule and is capable of detecting PTH levels in normal subjects as well as suppression of PTH after oral administration of calcium. The ICMA PTH assay has been shown to be adequate in the diagnosis of primary hyperparathyroidism and it could prove useful in monitoring renal failure patients and investigating other bone diseases such as osteoporosis.
