Radioimmunoassay of serum parathyrin: comparison of five commercial kits.

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.