Parathyroid hormone monitoring during total parathyroidectomy for renal hyperparathyroidism: Pilot study of the impact of renal function and assay specificity

Background: Commonly used assays for intact parathyroid hormone (iPTH) detect not only the biologically active 84-amino acid hormone [PTH(1-84)], but cross-react with an N-terminal-truncated fragment. Because iPTH assays often fail to predict success of parathyroidectomy in patients with renal hyperparathyroidism (rHPT), we compared results of a 3rd-generation PTH(184) assay (Bio-iPTH; Nichols Institute Diagnostics) with two 2nd-generation iPTH assays (from Nichols and Roche Diagnostics) by evaluating the PTH clearance kinetics during surgical treatment. Methods: We collected blood samples in short time intervals from 35 consecutive surgical patients with rHPT. Three patients had to be excluded from further calculations; the remainder were grouped according to kidney function and postoperative outcome. All, samples were analyzed with the 3 automated PTH assays, which have different specificities. Results: Twenty minutes after removal of the last gland, the PTH(1-84) values decreased to within the reference intervals in all patients with total and subtotal resection; however, iPTH concentrations normalized in only one half of these patients. In patients with poor renal function, the half-life of PTH(1-84) was shorter than the half-lives obtained with the iPTH assays. Conclusions: The accuracy of PTH monitoring during surgery for rHPT depends on renal function and assay specificity. All assays tested showed similar effectiveness in detecting missed glands, but the assay for PTH(1-84) gave more reliable results than the iPTH assays, which overestimated the concentration of PTH and hampered the intrasurgical diagnosis of resection sufficiency. (c) 2006 American Association for Clinical Chemistry.