A C-terminal radioimmunoassay for human parathyrin

Several features concerning the parathyrin (PTH) radioimmunoassay (RIA) in human serum have been considered. The bovine hormone (bPTH) was used as standard and to obtain the radioiodinated tracer and the antisera employed exhibited a C-terminal specificity. A modification of the classical Greenwood and Hunter method was used to label bPTH, based on the sequential addition of small amounts of Chloramine-T to the solution containing the hormone to prevent ovariodination. The purification by Quso G32 followed by a gel-filtration step, produced a suitable tracer for a highly sensitive RIA. Due to unespecific effects from serum in the incubation medium, serum concentration was rendered uniform in all of the assay tubes prior to the addition of the separation mixture (charcoal-dextran). The greatest sensitivity reached was 16 pg of bPTH in the incubation mixture with Ch 4M antiserum. This antiserum allows detection of immunoreactive PTH in the majority of normal subjects and has applicability to a wide range of bone disturbances.