Different routes bridging calcium in Japanese hemodialysis patients

There is growing evidence that not only serum calcium concentration but also excess calcium load is associated with vascular calcification and mortality in hemodialysis patients. Calcium load in hemodialysis patients cumulatively comes from three different routes: oral intake of calcium including calcium-based phosphate binders, traffic of calcium from/to dialysate, and calcemic action of vitamin D. The K/DOQI guidelines recommend sevelamer hydrochloride instead of calcium-containing phosphate binders to control serum phosphate concentration. However, in Japan, both kinds of phosphate binders are used concomitantly, mainly because Japanese patients are prone to a higher incidence of sevelamer-associated adverse events such as gastrointestinal symptoms. Regarding the calcium concentration of dialysate (D-Ca) in Japan, 3.0 mEq/L is more popular than 2.5 mEq/L. Calcium loaded through 3.0 mEq/L dialysate may lead to metastatic calcification rather than to bone formation because serum phosphate concentration rebounds several hours after the end of each hemodialysis session when plasma pH is still high. In contrast, use of 2.5 mEq/L dialysate may result in an unfavorable increase of intact parathyroid hormone particularly when the amount of oral calcium intake is reduced. Although a higher dose of vitamin D is required to counteract the stimulation of parathyroid glands, hypercalcemia is less likely with 2.5 mEq/L dialysate. As the new K/DOQI guidelines are released, it is time to discuss the appropriate D-Ca as well as doses and kinds of phosphate binders and vitamin D for the comprehensive management of Japanese hemodialysis patients.