Immunoreactive parathyroid hormone and calcitonin in plasma and ultrafiltrate before and after haemodialysis.

The effects of haemodialysis on circulating immunoreactive parathyroid hormone (iPTH) and calcitonin (iCT) were determined in relation to alterations in total (Ca) and ionized (Ca2+) plasma calcium. The hormones were measured in plasma, in dialysate and in ultrafiltrate in eight patients with elevated iPTH concentrations. There was a small, but significant reduction in plasma iPTH during haemodialysis concomitant with an increase in Ca and Ca2+. Only small changes were found in plasma iCT during dialysis. Ultrafiltrate iPTH concentrations were reduced from 46% of plasma values at the beginning of dialysis to 27% of plasma values at the end of 4 h dialysis. Gel chromatography of plasma and ultrafiltrate showed corresponding molecular profiles of intact iPTH and hormone fragments suggesting that none of the PTH peptides were restricted by the dialysis membrane. Clearance of intact iPTH (dialysance) was as expected according to molecular weight. From the PTH clearance we calculated that only 5 to 10 micrograms of intact hormone were removed during dialysis. We therefore conclude that the reduction in plasma iPTH during dialysis is probably related to a relative suppression of PTH secretion rather than due to loss of hormone during dialysis.