14 August 2002
The low calcium (Ca<sup>2+</sup>) dialysate have been developed to diminish the risk of hypercalcemia with the administration of active vitamin D and Ca<sup>2+</sup> carbonate as phosphate binder. Today, increasing numbers of hemodialysis (HD) patients have been on the low Ca<sup>2+</sup> dialysate (Ca<sup>2+</sup> = 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<sup>2+</sup> 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<sup>2+</sup> 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<sup>2+</sup> were found in spite of negative Ca<sup>2+</sup> balance. One month after change to the low Ca<sup>2+</sup> 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<sup>2+</sup>, Pi and Mg. This result indicates that the negative Ca<sup>2+</sup> balance during low-Ca<sup>2+</sup> hemodialysis-stimulated PTH secretion, which offset the decrease of serum Ca<sup>2+</sup>; a trade-off phenomenon between negative Ca balance and PTH. This suggests that low Ca<sup>2+</sup> dialysate may exaggerate the progression of secondary hyperparathyroidism.