We compared serum parathyrin radioimmunoassay data obtained with five commercially available kits for normal subjects, patients on dialysis, and patients with hyperparathyroidism. The Cambridge Nuclear kit gave low results, did not distinguish the dialysis-group sera from the normal sera, and had the greatest CV (56%) both inter- and intra-assay. The Immuno Nuclear PTH-II kit gave more satisfactory clinical data than their PTH-C-terminal kit; however, as with most procedures involving a substantial and variable nonspecific binding correction for each serum, parallelism between samples and the standard curve was poor, turnaround time slow, and inter-assay CV high (39%). Unlike the other kits, the Nichols and the Iso-Tex products depend on a direct methodology; they displayed good parallelism and distinguished among our three populations. A Scatchard plot of results with the Nichols kit was closest to the ideal linear model; the Iso-Tex kit had the shortest turnaround time.
Serum testosterone and especially free testosterone is one of the parameters commonly used to evaluate androgen excess or deficiency. The authors equilibrated serum samples with 14C-labeled testosterone followed by an ammonium sulfate precipitation to compare the "apparent free testosterone concentration" with "total" serum testosterone concentration in the following populations: normal males and females; females presenting with gynecologic problems, particularly hirsutism and/or virilization; and males and females on maintenance hemodialysis. Total serum testosterone for each specimen was assayed with five different commercially available RIA kits encompassing a variety of technics: direct assay technics, assays utilizing extraction procedures prior to RIA; tritium-labeled tracer as well as iodine-labeled tracers. Clinical correlations improve strikingly when apparent free testosterone concentrations rather than total serum testosterone concentrations are used.
A radioimmunoassay for parathyroid hormone is described that circumvents some previous difficulties. Parathyroid hormone binds strongly to other serum components. Consequently, a "control" curve is set up for each specimen, the specimen consisting of serum, diluent, and radiolabel, but no antibody. Final calculations are then based on the difference between the control curve and the curve obtained by incubating serum, diluent, radiolabel, and antibody. The lack of parallelism between various sample curves makes it almost mandatory that curves derived from at least 12 dilutions of serum be included for each specimen.
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