We investigated factors affecting net transperitoneal calcium balance (Ca-BL) and the level of parathyroid hormone in relation to stepwise changes in serum calcium, by short PET (peritoneal equibrium test during 240 min: using 2000 ml of 2.5% dextrose dialysate containing 1.75 mmol/L Ca) in uremic patients undergoing stable CAPD. We calculated Ca-BL (mg/effluent/PET) of 244 effluents obtained from 90 patients receiving calcium carbonate as a phosphate binder without vitamin D supplementation. Their serum calcium level corrected with albumin (cSCa), alkaline phosphatase activity (ALP) and intact-PTH level was 9.7±0.9 mg/dl, 236±83 mIU/ml and 153.0±172.4 pg/ml, respectively. We proposed two statistic significant regression lines between Ca-BL and total drainage effluent volume (Ca-BL-133X-0.056: r=0.981, P<0. 001), cSCa (Ca-BL=-12.9X+123.6: r=0.941, P<0.01). Total drainage volume (TDV) and cSCa were two major factors affecting Ca-BL. A TDV level of 2430 ml/240 min-PET or more was required for positive Ca-BL in cases with 9.5-10.0 mg/dl of cSCa, using this linear regression analysis. A cSCa level of 9.6 mg/dl or more was also required for positive Ca-BL in cases with 2400-2600 ml/240min-PET. We also proposed a significant linear regression line between the intact-PTH level and cSCa (i-PTH- -90. 5X+1015. 8, r=0.973, P<0. 01). This line suggest that 200 pg/ml of intact PTH was obtained by 9.0 mg/dl or less of cSCa level in 90 CAPD uremic patients. However, this cSCa level was difficult to obtain through CAPD therapy with the dialysate used (Ca=1.75 mmol/L) for positive net transperitoneal Ca-BL. In conclusion, the 1.75 mmol/L calcium dialysate may have induced relative secondary hypoparathyroidism with low turnover bone in CAPD uremic patients receiving calcium medication as a phosphate binder. We recommend the replacement therapy with less concentrated calcium dialysate for CAPD patients without a high parathyroid hormone level.
