weekly creatinine clearance ( wccr ) and kt / v are well - known parameters reflecting dialysis 
 dose and adequacy , and are applied to adjustment of the dialysis menu in each patient who 
 undergoes peritoneal dialysis ( pd ) . however , the limitations of these parameters in 
 predicting survival and morbidity have been reported . moreover , the collection of urine and peritoneal effluent 
 is cumbersome work not only for patients , but also for medical staff . estimated ccr ( eccr ) was proposed as an alternative marker for measured total ccr ( tccr ) , 
 because it is less expensive and time - consuming . but it was also reported that eccr calculated by the 
 cockcroft - gault formula substantially overestimated the effect of age on creatinine 
 excretion in pd patients . estimated glomerular filtration rate ( egfr ) is an alternative marker for measured gfr 
 ( mgfr ) , and it might be a possible indicator for prognosis in the general population without 
 known cardiovascular disease , diabetes or kidney disease and in ckd patients included in the modification of diet in 
 renal disease ( mdrd ) study . 
 moreover , these prognostic features of egfr might be partially independent of mgfr . we reported that egfr was well correlated with tccr in pd patients by cross - sectional 
 analysis . similar 
 correlation of egfr with ccr was reported by khosla , et al . , although the analyzed patients were 
 restricted to the population with a difference between two measurements of ccr of less than 
 25% . to clarify the actual utility of egfr in peritoneal dialysis practice , we retrospectively 
 collected the data from 21 pd patients at ja toride medical center for the period of one 
 year . patients who underwent pd at ja toride medical center for one year or longer were enrolled 
 in the study after their informed consent was obtained . pd patients with a treatment period 
 of less than a year , and patients who underwent combined pd and hemodialysis ( hd ) therapy 
 were excluded . to measure renal ccr , urine was collected for 24 hours ( from the second voiding of the day 
 before visiting the hospital to the first voiding on the day of visiting the hospital ) . pd 
 effluent was also collected for 24 hours on the day before visiting the hospital to measure 
 peritoneal ccr . the sum of the peritoneal and renal ccr was defined as the measured tccr . the serum , urine , and effluent cr were measured by the established enzyme method . the formula proposed by the japanese society of nephrology was applied for calculation of egfr as follows : egfr ( ml / min/1.73 m ) = 194  serum cr  age 
 (  0.739 in females ) protein catabolic rate ( pcr ) was calculated by the formula proposed by teehan as follows : pcr ( g / day ) = 6.25  ( urinary urea excretion + peritoneal urea excretion + 1.39 + 0.15 + 
 0.031  body weight in kg ) . pcr was normalized ( divided ) by the measured body weight ( bw ) and described as npcr 
 ( g / kg / day ) . according to the guidelines of the japanese ministry of health , labour , and welfare , 
 informed consent of the patients the study protocol was approved by the ethics 
 committee of ja toride medical center . the data are shown as means  sd , unless otherwise specified . to observe the correlation of 
 two sets of data , the pearson s correlation coefficients were calculated using excel 2007 
 ( microsoft , redmond , wa , u.s.a . ) . as table 1table 1characteristics of the studied patientsmen / women16 / 5age ( years)66.6  12.6 ( 4695)capd / apd13 / 8cause of ckddm7cgn7ns4others3treatment period of pd in months45.1  32.4 ( 14118)samples in the data analysis1145.4  1.5 ( 27 ) per patient shows , 21 patients met the inclusion criteria and were included in this study . the patients comprised 15 men and 6 women with an average age of 66.6  12.6 years ( 4695 
 years old ) , and their average pd period was 45.1  32.4 months ( 14118 months ) . their causes 
 of ckd were diabetes mellitus ( dm ) in seven patients , chronic glomerulonephritis ( cgn ) in 
 seven patients , nephrosclerosis ( ns ) in four patients , and others in three patients . continuous ambulatory pd ( capd ) was undertaken in 13 patients , and the other eight patients 
 received automated pd ( apd ) . during the period of one year from november 2010 to october 
 2011 , 114 data sets of egfr and tccr from the 21 patients were suitable for data analysis . 
 according to the analysis , egfr and tccr were correlated ( r. = 0.435 in figure 1figure 1egfr and tccr . the open circles in the plotted data were obtained from one patient 
 who denied the habitual intake of creatine supplements , such as creatine 
 monophosphate , but poorly complied with the diet therapy . ) . however , their correlation was less than that of a previous cross - sectional study 
 ( r. = 0.836 ) . unexpectedly 
 lower egfr levels were observed in one patient ( shown as open circles in figure 1 ) . repeated counseling of the patient revealed 
 that his diet fluctuated . as figure 2figure 2tccr - egfr difference and npcr ( a ) and total cr excretion and npcr ( b ) in one 
 patient who showed fluctuating diet intake . more detailed data from the patient , 
 exhibited as open circles in figure 1 are 
 shown . variations in the difference between egfr and tccr were correlated with both 
 total cr excretion and npcr . shows , tccr - egfr difference and total cr excretion were actually correlated with 
 npcr in this patient . similar correlations were observed for the difference between egfr and 
 tccr with total cr excretion ( r. = 0.821 in figure 
 3figure 3tccr - egfr difference and total cr excretion . differences between egfr and tccr were 
 well correlated with total cr excretion in total samples . ) and npcr ( r. = 0.636 in figure 4figure 4tccr - egfr and npcr . differences between egfr and tccr were correlated with npcr in 
 total samples . ) in all the data . total cr excretion and npcr were also correlated with each other 
 ( r. = 0.516 in figure 5figure 5total cr excretion and npcr . total cr excretion and npcr were also correlated with 
 each other in total samples . ) . the open circles in the plotted data were obtained from one patient 
 who denied the habitual intake of creatine supplements , such as creatine 
 monophosphate , but poorly complied with the diet therapy . tccr - egfr difference and npcr ( a ) and total cr excretion and npcr ( b ) in one 
 patient who showed fluctuating diet intake . more detailed data from the patient , 
 exhibited as open circles in figure 1 are 
 shown . variations in the difference between egfr and tccr were correlated with both 
 total cr excretion and npcr . tccr - egfr difference and total cr excretion . differences between egfr and tccr were 
 well correlated with total cr excretion in total samples . total cr excretion and npcr were also correlated with 
 each other in total samples . this retrospective study with the data collected for a year from 21 pd patients showed that 
 the correlation of egfr with tccr was less than that of a previous cross - sectional 
 study . the difference 
 between tccr and egfr was mostly dependent on total cr excretion , as reported in 
 pre - dialysis patients , but 
 this has never been reported in pd patients . moreover , total cr excretion fluctuated 
 according to the npcr . consequently , protein intake estimated by npcr may affect the 
 difference between tccr and egfr . because creatinine is homogeneously distributed in the body water , serum creatinine level 
 is determined by the balance of several factors , such as oral intake , generation in the 
 muscle , intrinsic degradation ( metabolic clearance ) and clearance by peritoneal dialysis and 
 the kidney ( figure 6figure 6considerable factors determining serum cr levels . meats ( per 100 g ) generally contain 
 400460 mg of creatine and creatinine ( see discussion for details ) . ) . the amount of creatinine obtained by oral intake is mainly dependent on the amount 
 of meat , which generally contains 400450 mg of creatinine and creatine per 100 g , or more 
 precisely , 1 mg of creatinine and 23 mg of creatine per 1 g of meat protein . actually , total cr excretion was 
 well correlated with npcr in this study ( figure 
 5 ) . meanwhile , the cr generation rate in the muscle is relatively stable , because it 
 is thought to be related to the muscle mass and activity . mainly 
 affects the variance in urinary creatinine excretion , especially in the case of preserved 
 residual renal function , which has a wider ranging capacity for compensation . consequently , 
 the serum cr concentration and its calculation product , egfr , are supposed to be more stable 
 parameters than ccr by diminishing the preserved capacity in small solutes clearance of the 
 kidney . the increased difference between tccr and egfr in the higher pcr population could be 
 explained by a similar reason , because pcr was positively correlated with total cr 
 excretion . hence , serum cr and its calculation product , egfr , may be superior to ccr because 
 they are less dependent on diet , unlike ccr . ( per 100 g ) generally contain 
 400460 mg of creatine and creatinine ( see discussion for details ) . recently , it has been reported that egfr had a prognostic value for ckd - related 
 complications , kidney failure , cardiovascular risk 
 factors and 
 mortality . it is possible 
 that egfr has a similar independency and distinct feature as a predictive indicator even in 
 pd patients . hence , the obtained value can fluctuate 
 as a result of several factors , such as patient condition , diet and drugs , which means that 
 mgfr should not always be considered a representative value or gold standard  of renal 
 function , or rather the 
 preserved capacity of the kidney to maintain the serum level of creatinine within a certain 
 range under conditions of fluctuating intake may be a more reasonable index for actual 
 kidney function . although the peritoneal clearance of small solutes represented by 
 creatinine should be taken into consideration in pd patients , egfr derived from serum creatinine , age and 
 gender may diminish the compensatory fluctuation of small solute clearance in the kidney , 
 and provide a more stable level in each pd patient . this feature may be valuable in routine 
 clinical practice , and it is worth investigating the significance of egfr as a possible 
 prognostic factor in pd patients , as reported in pre - dialysis patients , 
 . this study has some limitations . because the study design was a retrospective analysis at a 
 single center , the patient characteristics were divergent with respect to pd modalities , 
 exposure periods , residual renal function and adherence to diet therapy . in addition , the 
 study population was small , and equal amounts of data were not collected for each patient . therefore , differences between individual patients and the entire study population could not 
 be distinguished from the obtained data . however , fluctuating cr excretion was certainly 
 observed not only in data from individual patient but in all collected data , as shown in 
 figures 2 , 3 , 4 , 5 . this study revealed the practical profile of egfr , distinct from tccr , as a more stable 
 marker for small solutes clearance by dialysis and the kidney . a more extended and 
 longitudinal study will be needed to verify the actual value of egfr in pd practice .
objective : the usefulness of estimated glomerular filtration rate may not be 
 restricted to pre - dialysis patients , since we reported that estimated glomerular 
 filtration rate was well correlated with measured total creatinine clearance in peritoneal 
 dialysis patients . to clarify the clinical usefulness of estimated glomerular filtration 
 rate as a parameter for peritoneal dialysis adequacy , 
 we retrospectively surveyed 
 estimated glomerular filtration rate and total creatinine clearance in peritoneal dialysis 
 patients treated at ja toride medical center.patients and methods : a total of 114 data sets of estimated glomerular 
 filtration rate and total creatinine clearance from 21 pd patients treated at ja toride 
 medical center were collected from november 2010 to october 2011 . 
 the patients consisted 
 of 15 men and six women with an average age of 66.6  12.6 years ( 4695 years old ) . 
 the 
 average number of samples was 5.4  1.5 ( 2 to 7 ) per patient.results : the collected data showed less correlation of estimated glomerular 
 filtration rate and total creatinine clearance ( r. = 0.435 ) than that of a previous 
 cross - sectional study ( r. = 0.836 ) . 
 as reported in pre - dialysis patients , the differences 
 between estimated glomerular filtration rate and total creatinine clearance were 
 correlated with total creatinine excretion in urine and pd effluent ( r. = 0.821 ) . 
 the 
 differences were also correlated with normalized protein catabolic rate , which was one of 
 the main determinant factors for total creatinine excretion ( r. = 0.636 ) . 
 a similar 
 tendency was apparently observed in one patient with poor compliance to diet therapy and 
 fluctuating dietary intake . from the analysis of these data , serum creatinine seemed to 
 fluctuate less possibly due to compensatory capacity of the residual renal function in 
 small solute clearance.conclusions : consequently , estimated glomerular filtration rate was turned 
 out to be a more stable parameter than total creatinine clearance , which might be a 
 desirable feature in long - term follow - up of peritoneal dialysis patients .