Kinetic analyses of parathyroid hormone clearance as measured by three rapid immunoassays during parathyroidectomy

Abstract

Background: Rapid intraoperative parathyroid hormone (PTH) measurements are an important prerequisite for minimally invasive parathyroidectomy, serving as a feasible marker for "cure" because of the short half-life of PTH. Because automated analysis may facilitate monitoring, two automated PTH assays were compared with an established manual method. Methods: We collected 109 plasma samples during minimally invasive surgery on 20 patients with primary hyperparathyroidism and single-gland disease. PTH was analyzed manually with a test from Nichols and by two automated assays from Diagnostic Product Corporation (DPC) and Roche, respectively. PTH half-life and residual concentrations were calculated by two kinetic models. Results: Despite good overall correlations between methods [DPC = 1.07(Nichols) - 12 ng/L; r = 0.95, Sy|x = 26 ng/L and Roche = 1.16(Nichols) - 2.82 ng/L; r = 0.98; Sy|x = 16 ng/L], marked interindividual differences were observed. The iterative kinetic model failed with a nonuniform PTH decrease, but the interpolative model produced valid results. The mean (SD) half-life of 3.7 ± 1.4 min with DPC differed significantly (P <0.05) from the 4.3 ± 1.6 min with Roche (Nichols, 4.0 ± 1.6 min). DPC produced significantly lower mean residual PTH (15 ng/L) vs Roche (27 ng/L); Nichols results were between them (20 ng/L). However, these differences were clinically irrelevant. Conclusions: Automated methods are as suitable as the manual test. The preoperative baseline PTH is necessary but is insufficient for kinetic calculations. © 2002 American Association for Clinical Chemistry.