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adynamic bone disease and secondary hyperparathyroidism are associated with not only viability and quality of life ( qol ) but also mortality in long - term dialysis patients .
it is generally considered that ca and bone metabolism between peritoneal dialysis ( pd ) and hemodialysis ( hd ) patients provided remarkable differences according to dialysis modalities .
hemodialysis patients undergo rapid and intermittent removal of phosphate , uremic toxins and excess body fluid from sera , and influx or efflux of ca influent in such metabolism [ 13 ] .
higher serum ca levels and continuous glucose loading occur , which may lead to a higher incidence of adynamic bone in capd patients compared with that in hd patients [ 4 , 5 ] . patients with very low parathyroid hormone ( pth ) level had a higher mortality rate after adjustment for age , gender , diabetes , and dialysis vintage .
the turnover of bone remodeling in pd patients is lower than that in hd patients [ 4 , 5 ] . using
3.5  meq / l ca dialysate in hd , ca removal demonstrated a negative balance [ 7 , 8 ] .
it is recognized that ca mass transport in capd patients depends on the following factors : ca concentration in the dialysis fluid , starting plasma ca and p concentrations , and ultrafiltration , which removes the nonprotein bound diffusible calcium [ 912 ] .
characteristics of plasma solute transport in patients with automated peritoneal dialysis ( apd ) are resembled with that of hd .
effects of apd on residual urinary volume compared with that in capd were reported [ 13 , 14 ] .
it is postulated that a short - time dwell of peritoneal dialysate may lead to differences in the transperitoneal ca balance and pth secretion between apd and capd patients .  
the objective of the present study was to evaluate differences of transperitoneal ca balance between apd and capd patients without residual renal function .
twenty - three patients ( 15 males and 8 females ) took a standard peritoneal equilibrium test ( pet ) , and 24-hour peritoneal effluents ( pe ) were collected on capd for the determination of solute kinetics every year .
transperitoneal balance studies of calcium ( ca ) were examined for these anuric patients treated by pd .
the transperitoneal ca balance was calculated according to the formula for peritoneal mass transfer as follows : 
 ( 1)concentration  of  cadrained  volume  concentration  of  cainfused  volume .
a routine peritoneal equilibration test ( pet ) using 2.5% dextrose pd solution was performed after the initiation of pd in new patients and every 12 months thereafter .
pet results were used for the patients in order to choose the optimized pd prescriptions .
pd effluents were obtained just before the pet and at 4 hours as the long - time and short - time dwell samples . in uremic patients and non - ckd patients ,
the ethics committee of juntendo university faculty of medicine approved this study including evaluation of peritoneal morphology and peritoneal function . statistical analysis consisted of both simple and multiple linear regressions .
relationships between ultrafiltration and transperitoneal ca removal were analyzed with spearman 's correlation coefficient test .
basic characteristics of participants are shown in table 1 . mean age of patients was 51.1  14.9 years old .
dairy average dosage of caco3 was 3.44  2.57  g. average dialysate ca concentration in apd patients was 6.10  0.94 .
eleven apd patients used low - calcium pd solution in order to suppress elevation of serum ca .
eleven peritoneal effluents ( pe ) for 24 hours on apd and 23 pes on capd were collected in the same patients ( table 2 ) .
there was no significant difference in the ca concentration of pd solution between apd and capd .
we obtained 24-hour collected pe on apd and capd on consecutive days in 23 pd patients .
1.37  63.18  mg of ca was absorbed from pd solution on apd , whereas 67.1  58.6  mg of ca was removed on capd ( table 3 ) .
calcium was removed on capd ; however , the ca removal indicated zero on apd , using the same ca concentration pd solution and removing the same amount of body fluid , respectively , ( p < 0.01 , figure 1(a ) ) . during night peritoneal dialysis ( npd ) , ca was absorbed from pd solution ( figures 1(a ) and 1(b ) ) .
calcium removal in pd patients using 2.5% dextrose dialysate containing 7.0  mg / dl of ca is shown in table 4 .
the levels of intact pth were remarkably increased at 4 hours of pet ( from 170.2  161.5  pg / ml to 201.1  181.3  pg / ml , p < 0.002 ) .
transperitoneal ca removal and ultrafiltration showed a significant positive relationship both in short - time and long - time dwell ( figure 2 , coefficient value = 0.367 , p < 0.02 ) .
meanwhile , there was no relationship between ca removal and ultrafiltration in long - time dwell .
we demonstrated that transperitoneal ca removal in apd patients without residual renal function was smaller , compared with that in capd patients .
in the same patients , the ca removal in apd was significantly lower than that in apd .
the solute and body fluid kinetics have been shown to be quite different between capd and hd [ 2 , 3 ] .
factors influencing calcium removal during dialysis are as follows : ( 1 ) ultrafiltration rate , ( 2 ) concentration of serum ionized calcium at starting of dialysis session , ( 3 ) concentration of serum inorganic phosphate at the start , and ( 4 ) concentration of dialysate calcium [ 912 , 15 , 16 ] . the levels of serum ca and phosphorous in hd patients fluctuated , contributing to intermittent and rapid removal of solute and body fluid
; meanwhile , constant solute and body fluid kinetics were major characteristics of capd therapy .
exchanges and removal of minerals and small molecule solutes were rather drastic during npd and steady during day - time dwell in continuous cyclic pd ( ccpd ) patients .
since dialysate ca concentration influences ca balance during hd and capd , active vitamin d and calcium - containing phosphate binders regulating serum ca concentration require a reduction in dose , from 1.75 to the more physiological dialysate ca concentration [ 1 , 7 , 8 , 1719 ] .  
the present study showed that the dwell time and ultrafiltration played crucial roles in transperitoneal ca removal in pd patients .
ca removal in long - time dwell was independent on ultrafiltration , whereas ultrafiltration increased ca removal in short - time dwell . according to the results
, it appears that smaller amount of ca - containing phosphate binder in apd patients can be administrated compared with that in capd patients .
the average concentration of dialysate ca was 6.1  mg / dl , and all participants used low - calcium dialysate at least one or two bags to prevent the elevation of serum ca .
the level of pth markedly increased during pet , but not the elevation of pth ( data not shown ) in this study .
however , the slight ca change contributing to ultrafiltration might be a stimuli of pth secretion .
this study showed the characteristics of the ca removal in anuric apd patients as being somewhere between that of capd and hd . short - time dwell and frequent dialysate exchanges during npd suppressed the transperitoneal ca removal in apd patients
; it appears that the levels of serum ca increase easily in anuric apd patients using calcium - containing phosphate binder .
backgrounds . calcium ( ca ) and bone metabolism in continuous ambulatory peritoneal dialysis ( capd ) and hemodialysis ( hd ) patients show a remarkable difference depending on dialysis modalities . 
 the levels of serum ca and phosphate ( p ) in hd patients fluctuate contributing to the intermittent and rapid removal of plasma solute unlike in capd . 
 characteristics of plasma solute transport in automated peritoneal dialysis ( apd ) patients are resembled with that in hd . 
 the purpose of the present study was to examine the difference of transperitoneal ca removal between apd and capd anuric patients . 
 subjects and methods . 
 twenty - three apd anuric patients were enrolled in this study . 
 biochemical parameters responsible for transperitoneal ca removal in 24-hour and 4-hour peritoneal effluents were analyzed on capd and apd . 
 results . 
 transperitoneal ca removal on apd was smaller compared with that on capd . 
 the ca removal was related to the ultrafiltration during short - time dwell . 
 decrease of the ca removal during npd induced by short - time dialysate dwell caused negative or small ca removal in apd patients . 
 the levels of intact pth were increased at the end of pet . 
 conclusion . 
 it appears that short - time dwell and frequent dialysate exchanging might suppress the transperitoneal ca removal in anuric apd patients .