it is well known that the kidney size of the patient undergoing chronic hemodialysis ( hd ) gradually decreases . however , only a few reports are there on the study of the actual decrease rate [ 24 ] . on the other hand , scheduled ultrasonographic ( us ) examination of kidney after induction of hd is important to check the progression of acquired cystic disease of kidney ( acdk ) and renal cancer which may arise in acdk [ 5 , 6 ] . we examined the renal longest diameter of chronic hd patient at the scheduled us kidney checkup , calculated the alteration rate of the size in the same patients , and studied the difference of the alteration rate among the factors such as gender , age , and original diseases . of 229 outpatient chronic hemodialysis patients , 109 patients , who had neither hereditary polycystic disease nor severe acquired cystic disease of kidney , were selected ; we performed ultrasonography ( us ) twice or three times to measure their maximum renal diameter ( mean of both kidneys ) , and the yearly alteration rate of the diameter was calculated . the largest caliber of the imaged kidney was measured using the measurement tool loaded in the us machine ( aroca ssd-280 , toshiba nemio 30 , japan ) ( figure 1 ) . the us study of the kidney was mainly carried out intercostal method through ribs with 3.75  mhz linear probe . some of the patient 's data had been measured more than three times , and for those cases , the longest interval between the two data was used for calculation . the yearly alteration rate ( cm / year ) was calculated as follows : { ( mean of both kidney diameter ( kd1  kd2  cm))/measurement interval ( month ) }  12 ( months ) . the results were studied to find out the factors that may influence the alteration rate of kidney diameter : age , gender , and the original disease ( compared among three groups , chronic glomerulonephritis and iga nephropathy , diabetes , and others including hypertension ) . to evaluate whether the alteration rate was stable all through the  on hd period  or not , patients were divided to nine groups according to the interval from the induction of hd to the first measurement . and all patients agreed with signature that their clinical data or physical findings would be used for statistical study of the japanese society for dialysis therapy , and other clinical studies . this study did not violate ethical standards of the declaration of helsinki and its revisions , because the measurements were performed during the annual routine health check up for hd patients without any additional invasive procedures , and the purpose of the measurement was explained by the examiner and verbal allowance was obtained by the patient at the time of examination . statistical evaluations of various parameters were performed using stat view 4.5 for mac ( abacas concepts , inc . ca usa ) , and each analytical method was indicated in the table . a p value of < 0.05 was regarded as statistically significant . raw data obtained by all 109 patient 's measurements and connected in line between the same patient 's data plots is indicated as in figure 2 . the average interval from the induction of hd to the first measurement was 29.5  2.5 months ( from 0.6 to 114 months ) , and the average interval of the two measurements was 35.9  2.2 months ( from 5.8 to 86 months ) . the average of all measured renal largest diameter was 6.91  0.06  cm ( 4.3 to 11.1  cm ) . the average decrease rate of renal diameter was 4.34  0.4  mm / year , which was simply obtained from the mean of 109 patients ' results . among the three original groups , cgn + iga and diabetes groups were younger than ht + others group ( p < 0.05 ) , and diabetes group showed larger renal diameter at the first measurement ( p < 0.05 ) as indicated in table 1 . however , no difference was seen on the decrease rate in relation to gender , age , and original disease ( tables 1 and 2 ) . comparing the samples those were divided to 9 categories according to the time of the first measurement after induction of hd , the decrease rate was large when the hd vintage was small , suggesting that the alteration rate reduced according to the duration of hd ( 5.3  0.8  mm / year , n = 33 , first measurement not more than 10 months after induction of hd , 3.9  0.6  mm / year , n = 18 , ~20 months , 5.4  0.9  mm / year , n = 16 , ~30 months , 4.9  3.5  mm / year , n = 6 , ~40 months , 3.3  1.0  mm / year , n = 11 , ~50 months , 3.6  0.8  mm / year , n = 11 , ~60 months , 2.1  1.3  mm / year , n = 5 , ~70 months , 0.6  0.6  mm / year , n = 5 , ~80 months , 1.5  1.6  mm / year , n = 4 , and ~80 , p = 0.014 , kruskal - wallis ) as indicated in figure 3 . although gradual decrease of the kidney size is frequently observed in hd patient , to the best of our knowledge , no studies have been found in the english medical literature reporting the actual decrease rate of the kidney size by measuring the same patient consecutively . therefore , the decrease rate and the influence of original disease on the decrease speed , were poorly understood . our study indicated that kidney size decreased approximately 4  mm per year in an average , and the decrease rate slowed as the dialysis vintage increased . original disease , gender and age did not affect the decrease rate .   in the japanese literature , uchida   studied on hd patients concerning kidney size , degree of cysts formation and possibility of cancer formation from the autopsy and surgical specimens . they reported that kidney size decrease the first three years after the induction of hd ( kidney size ( cm ) = k = 9.13  0.33x ( years ) ) , then , increased due to acdk formation until 8 years ( k = 5.43 + 0.15x ) , and after 8 years , kidney size decreased again ( k = 7.62  0.58x ) . yamaguchi et al .   reported from us observation , that kidney size decreased the first three years after the induction of hd , kept the same size until 8 years , and then start to increase size due to acdk formation . according to their study , the renal shrink rate of patients who had diabetes was smaller than those who had other diseases in the first 5 years from induction of hd . these studies were not suitable to evaluate the common decrease rate of renal size after induction of hd , that in they include both cystic and noncystic kidneys [ 13 ] . we excluded 125 acdk - formed patients out of 234 patients and evaluate 109 patients . our study did not consider the initial renal diameter at the induction of hd , as there was no data , and it would be better if the measurement interval had been regular to obtain more accurate data . the shrinkage of kidney is thought to not start at the induction of hd but at the histological change into end - stage kidney by original diseases . other previous study reported that the renal diameter of the patients having diabetes was larger than that of those having other diseases such as cgn . renal hypertrophy is thought to one of the signs of renal impairment of diabetic nephropathy [ 8 , 9 ] . the decrease rate of renal diameter in patients who have diabetes is reported to be faster than in those who have other diseases in the beginning of hd . in our study , the mean of the first measured renal diameter of the diabetic patients was also larger than that of other original diseases as indicated in the table 2 . however , according to our study , there were no difference in the decrease rate of renal size among the original diseases . some cases showed different types of renal cortical shrinkage such as the increase of parapelvic adipose tissue , not altering total renal diameter so much . there were no malignant tumors in our study including acdk case , though they were excluded from the calculation of renal size . although more study will be needed to find out the relation between tumor formation and alteration of renal appearance , our study suggested that macroscopic change of end - stage kidney would be almost the same among the original diseases that were responsible for inducing hd . chronological change of renal size on chronic hd was studied for 109 hd patients using us examination consecutively . renal diameter decreased approximately 4.3  mm each year , and the decrease rate slowed as the duration of hemodialysis increased . the decrease rate was not affected by the original disease , age , and gender .
we here present the results of ultrasonographic ( us ) evaluations on the alteration of renal diameter of chronic hd patients . of 109 outpatient hd patients who had neither severe acquired cystic disease of the kidney nor hereditary polycystic kidney disease 
 , we performed us two or three times to measure their maximum renal diameter ( mean of both kidneys ) , and the yearly alteration rate was calculated . 
 the average interval of the two measurements was 35.9 months , and the average hd duration from the hd induction to the first measurement was 29.5 months . 
 the average decrease rate of renal diameter was 4.34  0.4 ( se ) mm / year . 
 no statistical difference was seen on the decrease rate in relation to gender , age and original disease ( among three groups , glomerulonephritis and iga nephropathy , diabetes , and others including hypertension ) . however , the decrease rate was large when the first measurement was close to the induction of hemodialysis , suggesting that the alteration rate reduced according to the hemodialysis vintage ( 5.3  0.8  mm / year , first measurement not more than 10 months after induction of hd and 1.5  1.6  mm / year , first measurement more than 80 months after induction of hd ) . 
 renal diameter decreased approximately 4.3  mm each year , and the decrease rate slowed as the length of time on dialysis increased .