Effect of one haemodialysis treatment on the plasma concentrations of intact parathyroid hormone and ionised calcium: usefulness of end-dialysis values in evaluating the suppressibility of hyperparathyroidism.

We studied the effect of one haemodialysis treatment on the plasma concentrations of intact parathyroid hormone (PTH), total immunoreactive PTH (determined with an antibody against the mid-molecular part of the hormone), and ionised calcium in 25 patients on maintenance dialysis for chronic renal failure. During dialysis the calcium concentration in the external fluid was 1.75 mmol/l, which led to an increase in the plasma ionised calcium concentration from 1.23 +/- 0.07 mmol/l (mean +/- SD) at commencement of dialysis to a final 1.35 +/- 0.07 mmol/l (P less than 0.001). The plasma concentration of intact PTH decreased from 27.4 +/- 26.3 pmol/l to 13.0 +/- 19.1 pmol/l (P less than 0.001) during the treatment. Total immunoreactive PTH did not change, reflecting poor dialysability of PTH and PTH fragments. We also compared the dialysis-induced changes in the plasma concentrations of intact PTH and ionised calcium with those induced by a calcium infusion test. We conclude that in the majority of dialysis patients, one haemodialysis treatment with a relatively high external fluid calcium concentration can be used to assess the suppressibility of secondary hyperparathyroidism.