Technical and clinical characterization of the Bio-PTH (1-84) immunochemiluminometric assay and comparison with a second-generation assay for parathyroid hormone

BACKGROUND: The Bio-Intact parathyroid hormone (1-84) assay (Bio-PTH), a newly developed two-site immunochemiluminometric assay, measures exclusively PTH (1-84) in contrast to second-generation "intact PTH" (I-PTH) assays. We investigated the technical performance and clinical significance of this new assay. METHODS: PTH was measured simultaneously by the Bio-PTH assay and Allegro intact PTH IRMA in sera from Japanese patients with calcium disorders. RESULTS: Measured Bio-PTH in serum was unaffected by six freeze-thaw cycles and was stable at 4 degrees C for 7 days and during storage at -20 or -80 degrees C over 28 days. The calibration curve was linear to 1800 ng/L. The detection limit was 3.9 ng/L. The intra- and interassay imprecision was <2.8% and 3.5%, respectively, for analyte concentrations spanning the range of the calibration curve. Bio-PTH was unaffected by a 1000-fold excess of PTH (7-84), although I-PTH reacted equally with PTH (7-84) and PTH (1-84). Bio-PTH was correlated with I-PTH in healthy individuals (r = 0.953; P <0.0001; n = 26) and in the full population without renal dysfunction (r = 0.994; P <0.0001; n = 62). In 72 volunteers, mean (SD) Bio-PTH was 22.2 (7.1) ng/L, or 62% of the mean I-PTH 36.1 (22.3) ng/L]. This ratio was 51% in hemodialysis patients (n = 177). Mean Bio-PTH was high in patients with primary hyperparathyroidism 121 (85) ng/L; n = 18] and hemodialysis patients 102 (104) ng/L; n = 177], low in idiopathic hypoparathyroidism 5.5 (2.8) ng/L; n = 4], and within 2 SD of the mean for healthy controls in Paget disease of the bone 34 (15) ng/L; n = 9] and bone metastasis 24 (12) ng/L; n = 8]. CONCLUSION: The Bio-PTH assay is sensitive and precise and produces expected results for patients with the studied disorders of calcium metabolism.