The negative Ca(2+) balance is involved in the stimulation of PTH secretion

Abstract

The low calcium (Ca(2+)) dialysate have been developed to diminish the risk of hypercalcemia with the administration of active vitamin D and Ca(2+) carbonate as phosphate binder. Today, increasing numbers of hemodialysis (HD) patients have been on the low Ca(2+) dialysate (Ca(2+) = 2.5 mEq/l). However, the clinical consequences of a negative calcium net-balance which may be induced by the use of low Ca dialysate are not well evaluated. In the present study, we explored the effects of low Ca(2+) dialysate on the calcium balance and the PTH secretion. Eighty one chronic HD patients (male/female: 47/34; mean age: 60.2 +/- 1.5 years; mean HD periods: 11.1 +/- 0.8 years) who had been dialyzed with 3.0 mEq/l Ca(2+) dialysate were studied. All patients were transferred to the low Ca dialysate, which actually brought about a negative net-balance in Ca (mean: -94.5 mg) and an increase in serum intact PTH levels (mean: +23.7%: p = 0.03) during a single HD session. However, no changes in serum ionized Ca(2+) were found in spite of negative Ca(2+) balance. One month after change to the low Ca(2+) dialysate (total 12 sessions in each case), serum intact PTH levels increased significantly (186.7 +/- 19.5 vs. 216.2 +/- 21.9 pg/ml: p = 0.01) in spite of the fact that no changes were found in serum ionized Ca(2+), Pi and Mg. This result indicates that the negative Ca(2+) balance during low-Ca(2+) hemodialysis-stimulated PTH secretion, which offset the decrease of serum Ca(2+); a trade-off phenomenon between negative Ca balance and PTH. This suggests that low Ca(2+) dialysate may exaggerate the progression of secondary hyperparathyroidism.