DEVELOPMENT OF A C-TERMINAL-REGION-SPECIFIC RADIOIMMUNOASSAY OF PARATHYROID HORMONE-RELATED PROTEIN

Few data are published regarding the molecular forms or concentrations of circulating and urinary parathyroid hormone-related protein (PTHrP) in normal subjects and patients with humoral hypercalcemia of malignancy (HHM). We have developed a C-terminal-region-specific radioimmunoassay for human PTHrP 109-141 (C-PTHrP radioimmunoassay) using a sheep antiserum immunized with a novel synthetic human PTHrP 109-141 for immunogen and a novel synthetic [Tyr108]PTHrP 108-141 for radiolabel. The detection limit of this assay is 2 pM for human PTHrP 109-141 and is sensitive enough to detect circulating and urinary C-PTHrP in normal subjects. The average immunoreactive concentration of serum (n = 76) and urinary (n = 12) C-PTHrP in normal subjects are 31.4 +/- 7.4 pM and 322.9 +/- 67.2 pM, respectively. Levels in patients with HHM are significantly elevated when compared to controls. This assay may be useful in the differential diagnosis of hypercalcemia.