Background: The so-called "intact parathyroid hormone (iPTH)" assay detects large C-terminal PTH fragments that are lacking several N-terminal amino acid residues in addition to 1-84 PTH molecules.
Methods: Blood samples were obtained from 65 predialysis patients (male, 35; female, 30) and 109 dialysis patients (male, 73; female, 36). The plasma 1-84 PTH levels were determined by a specific immunoradiometric assay (IRMA).
Results: The ratio of 1-84 PTH/iPTH did not show a significant correlation with glomerular filtration rate (GFR) among patients with a GFR of more than 80 ml/min, while it showed a positive correlation with GFR among patients with a GFR of less than 80 ml/min. The ratio of 1-84 PTH/iPTH demonstrated a significant tendency to decrease in the order of patients with normal renal function (0.928 +/- 0.182), those with renal dysfunction (0.836 +/- 0.186; P < 0.05 vs patients with GFR > 80 ml/min [i.e., normal renal function]), and those with maintenance hemodialysis (0.618 +/- 0.123; P < 0.01 vs patients with GFR > 80 ml/min). The plasma levels of 1-84 PTH and conventional iPTH showed a close correlation in dialysis patients. Neither 1-84 PTH levels nor secondary parameters calculated from them showed a better correlation with bone metabolic markers than iPTH levels.
Conclusions: Circulating large C-terminal PTH fragment levels are increased in uremic patients. However, this noninvasive study failed to demonstrate the superiority of the specific 1-84 assay compared with the conventional iPTH assay to evaluate bone metabolism.