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

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, S(y/x) = 26 ng/L and Roche = 1.16(Nichols) - 2.82 ng/L; r = 0.98; S(y/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.