of all the patients admitted to beijing children s hospital between 2003 and 2007 , the incidence of urinary tract stones complicated by renal failure is only 0.05 to 0.45% . in 2008 , a sharp increase of children diagnosed as urinary calculi complicated by acute obstructive renal failure was noticed in beijing children s hospital , the biggest children s hospital in china . melamine contamination of infant formula was identified as the cause of the renal stones . according to a report from the chinese ministry of health in december of 2008 , 22,384,000 examinations were conducted in infants in china with suspected melamine exposure . by the end of november , 294,000 infants were diagnosed as having urinary tract stones and 51,900 infants were hospitalised . in beijing children s hospital , of all the screened children , 2.9% had urinary tract calculi , of which 4.2% were hospitalised , and 25 of the hospitalised children were subsequently diagnosed as urolithiasis with complication of acute obstructive renal failure . all of the 25 children had consumed the same brand of infant formula , sanlu , which was contaminated with melamine . the aim of the current study was to describe the clinical and laboratory features , the composition of calculi , the treatment and outcome of the 25 inpatients with melamine - induced kidney stones complicated by acute obstructive renal failure . from march 15th to november 17th in 2008 , 25 inpatients diagnosed as urinary tract calculi and acute obstructive renal failure in beijing children s hospital were enrolled in this study . the following data were collected : clinical signs , estimated consumption of contaminated formula , urinalysis , ultrasonography of the urinary tract , routine serum chemistry and haematology parameters , including serum urea nitrogen and creatinine , as well as treatment regimens , response to the treatments , duration of hospitalisation and outcome at 12 to 17  months follow - up . removed calculi were qualitatively and quantitatively analysed by high - performance liquid chromatography coupled with mass spectrometry , gas chromatography coupled with mass spectrometry and fourier transform infrared spectrometry . three therapeutic regimens were assessed : cystoscopy and retrograde catheterisation , dialysis ( peritoneal and haemodialysis ) , and fluid administration . the main outcome measures were : cure ( renal function returned to normal and all urinary tract calculi were removed ) , effective ( renal function returned to normal and urinary tract calculi decreased in size ) and ineffective ( urinary tract calculi did not decrease in size ) . urinalysis and ultrasound results were recorded every month and serum values of blood urea nitrogen ( bun ) , creatinine and uric acid were recorded every 3  months . a total of 25 chinese patients were included in this study ( 17 boys and eight girls ) . they were between 6  months and 3  years old , of whom 19 patients were under 1  year and six patients were between 1 and 3  years old . the median duration of exposure to sanlu infant formula was 9.5  months ( range 15  days to 24  months ) . the median duration of hospitalisation after stone detection was 14  days ( range 4 to 60  days ) . two patients had haematuria , eight had fever and 12 vomitted , plus diarrhoea or other gastrointestinal tract symptoms , e.g. bloating , abdominal pain , anorexia . ultrasound examination showed that the calculi were usually present in the following two appearences : sand - like crystals , either solitary or in clusters , with no shadow or with a comet - tail - like shadow ( fig . 1 ) ; or as larger size , clump - like calculi with a light shadow ( fig .  2 ) . most of the calculi are located in the renal pelvis and calyces , and at the three stegnosis sites of the ureter : the pyeloureteric junction , the site where the ureter spans the iliac blood vessels and the site where the ureter attaches to the bladder . 1image of the kidney ( ultrasonography ) : female , 8  months old , right kidney profile . a 0.15-cm sand - like calculus ( marked with + ) at the renal calyx with a comet - like tailfig . 2image of the kidney ( ultrasonography ) : male , 10  months old , left kidney profile . the 0.6    0.4-cm calculus at the renal calyx has a light shadow image of the kidney ( ultrasonography ) : female , 8  months old , right kidney profile . a 0.15-cm sand - like calculus ( marked with + ) at the renal calyx with a comet - like tail image of the kidney ( ultrasonography ) : male , 10  months old , left kidney profile . the 0.6    0.4-cm calculus at the renal calyx has a light shadow renal functions were significantly impaired in all of the patients : bun ranged from 14.7 to 49.0  mmol / l , creatinine ranged from 93.0 to 908.0 mol / l , serum potassium ranged from 2.94 to 7.91  mmol / l and serum uric acid ranged from 195.0 to 1,257.0  mol / l ( table  1 ) . 
 table  1specific data on each of the 25 infants hospitalised for melamine - induced kidney stones complicated by acute obstructive renal failurenumbergenderage ( months)duration of consuming the milk ( months)main symptomsstone positionsize of stones ( total , cm)serum potassium(mmol / l)bun ( mmol / l)cr ( mol / l)serum uric acid ( mol / l)treatmenteffect1m1313dysuria , fever1341.675.3520.5370.0727ceffective2f75anuria , fever120.835.6830.6467.0300ceffective3m2020abdominal pain , oliguria234.6018.8305.9546ceffective4m1212anuria , fever1341.437.9130.7355.0537ceffective5f84vomit , oliguria , fever346.2214.793.0793ceffective6f84vomit , diarrhoea , anuria341.923.7230.0534.0706feffective7m88vomit , oliguria , fever1342.695.9623.7420.0815pdeffective8m77anuria241.618.1249.0908.0635pdcure9m66anuria , fever341.585.6827.5448.31,108pdeffective10m106oliguria20.995.6716.1164.8833ceffective11m2020vomit , anuria , abdominal distention121.795.7339.7711.0647ceffective12f80.5anuria1342.225.5724.7575.91257pdeffective13m77oliguria , abdominal distention2340.345.7821.0248.8820fcure14m1717anuria341.142.9418.0181.5952ceffective15m77diarrhoea , haematuria , oliguria140.775.1022.4387.4830pd + ceffective16m1313diarrhoea , vomit , anuria121.125.4223.5381.01,247feffective17m77anuria12341.786.4825.6375.0614pdcure18f88diarrhoea , oliguria1242.586.3430.5854.0993pd + ccure19m2212anuria , fever2340.954.4626.8670.9940pdeffective20f106vomit , oliguria , fever44.8619.5157.0195feffective21m127anuria141.215.5921.0290.0709feffective22m3624anorexia , oliguria240.424.9427.7439.0439hdcure23f1111haematuria , oliguria1242.608.8447.3598.0621ceffective24f1111dysuria241.355.5719.1166.1442fcure25m82anorexia , oliguria10.104.5321.3194.3769fcurestone position : 1 . pelvis and calyces renalestreatment : c cystoscopy and retrograde catheterisation ; pd peritoneal dialysis ; hd haemodialysis ; f fluid administration specific data on each of the 25 infants hospitalised for melamine - induced kidney stones complicated by acute obstructive renal failure stone position : 1 . ureter attaching to the bladder ; 4 . pelvis and calyces renales treatment : c cystoscopy and retrograde catheterisation ; pd peritoneal dialysis ; hd haemodialysis ; f fluid administration toxicologic analysis to determine the composition of seven of the expelled calculi was performed . 3 ) were detected in all the calculi in a molar ratio of 1 : 1.2 to 1 : 2.1 . 3total ion chromatography of high - performance liquid chromatography  mass spectrometry ( lcms ) and mass spectrogram of uric acid ( detected in negative ion mode ) total ion chromatography of high - performance liquid chromatography  mass spectrometry ( lcms ) and mass spectrogram of uric acid ( detected in negative ion mode ) exposure to the contaminated milk formula was stopped immediately . correcting electrolyte abnormalities children with acute obstructive renal failure and oliguria for at least 2  days or anuria for at least 1  day were dialysed until clinical their chemistry parameters returned to reference ranges . surgical interventions to remove the stones were given to the patients with severe hydronephrosis and to the anuric patients in whom dialysis was ineffective or unsuitable . in our study , 11 patients ( 44% ) underwent cystoscopy and retrograde catheterisation ; seven ( 28% ) patients were dialysed , of whom six received peritoneal dialysis and one was haemodialysed ; and the remaining seven patients ( 28% ) received only fluid administration for 4 to 20  days . the solutions of 11.4% sodium bicarbonate were administered intravenously once or twice daily at a dose of 2  ml / kg to these patients and they were encouraged to drink plain water . their urine ph values were continuously monitored for them to reach 6.57.0 . before fluid administration , the stone sizes ranged from 0.10 to 1.92  cm ( by ultrasound ) , but after alkalisation , they reduced to 0 to 1.72  cm . the renal functions returned to normal within 7  days ( median 3  days ) in all of the patients . creatinine concentrations decreased to normal concentrations in 3.5    1.89  days in the cystoscopy group , in 3.8    2.26  days in the dialysis group and in 2.7    1.60  days in the patients receiving fluids . according to the criteria we mentioned earlier in this article , six of the 25 patients were cured and 19 were effective by the time of discharging . twenty - two patients were reviewed from may 1st 2008 to september 5th 2009 ; three patients failed the follow - up because of changes of address . at follow - up visits , all of the 22 patients had normal renal function and normal urine routine . 68% of the patients were found to have no urinary tract calculi at 3  months follow - up , 90% at 6  months and hydronephrosis or other sequelae were not identified . to the two patients who still had calculi after 6  months , potassium sodium hydrogen citrate granules ( 1  g / day , oral ) was given . after that , one patient had no stones at 8  months and the other had his calculi decreased in size . the latter was an 8-month - old boy with the largest stone ( 2.69  cm ) . eleven months after discharge from our hospital , the size of the stone was still quite big ( 1.20  cm ) , then , ultrasound - guided extracorporeal shockwave lithotripsy was given to this patient successfully . till now ( 15  months follow - up ) , no stones were found by urinary tract ultrasonography , and the urinalysis and renal function of the patient remained normal . 4follow - up of 22 of the patients follow - up of 22 of the patients a total of 25 chinese patients were included in this study ( 17 boys and eight girls ) . they were between 6  months and 3  years old , of whom 19 patients were under 1  year and six patients were between 1 and 3  years old . the median duration of exposure to sanlu infant formula was 9.5  months ( range 15  days to 24  months ) . the median duration of hospitalisation after stone detection was 14  days ( range 4 to 60  days ) . two patients had haematuria , eight had fever and 12 vomitted , plus diarrhoea or other gastrointestinal tract symptoms , e.g. bloating , abdominal pain , anorexia . ultrasound examination showed that the calculi were usually present in the following two appearences : sand - like crystals , either solitary or in clusters , with no shadow or with a comet - tail - like shadow ( fig . 1 ) ; or as larger size , clump - like calculi with a light shadow ( fig .  2 ) . most of the calculi are located in the renal pelvis and calyces , and at the three stegnosis sites of the ureter : the pyeloureteric junction , the site where the ureter spans the iliac blood vessels and the site where the ureter attaches to the bladder . 1image of the kidney ( ultrasonography ) : female , 8  months old , right kidney profile . a 0.15-cm sand - like calculus ( marked with + ) at the renal calyx with a comet - like tailfig . 2image of the kidney ( ultrasonography ) : male , 10  months old , left kidney profile . the 0.6    0.4-cm calculus at the renal calyx has a light shadow image of the kidney ( ultrasonography ) : female , 8  months old , right kidney profile . a 0.15-cm sand - like calculus ( marked with + ) at the renal calyx with a comet - like tail image of the kidney ( ultrasonography ) : male , 10  months old , left kidney profile . the 0.6    0.4-cm calculus at the renal calyx has a light shadow renal functions were significantly impaired in all of the patients : bun ranged from 14.7 to 49.0  mmol / l , creatinine ranged from 93.0 to 908.0 mol / l , serum potassium ranged from 2.94 to 7.91  mmol / l and serum uric acid ranged from 195.0 to 1,257.0  mol / l ( table  1 ) . 
 table  1specific data on each of the 25 infants hospitalised for melamine - induced kidney stones complicated by acute obstructive renal failurenumbergenderage ( months)duration of consuming the milk ( months)main symptomsstone positionsize of stones ( total , cm)serum potassium(mmol / l)bun ( mmol / l)cr ( mol / l)serum uric acid ( mol / l)treatmenteffect1m1313dysuria , fever1341.675.3520.5370.0727ceffective2f75anuria , fever120.835.6830.6467.0300ceffective3m2020abdominal pain , oliguria234.6018.8305.9546ceffective4m1212anuria , fever1341.437.9130.7355.0537ceffective5f84vomit , oliguria , fever346.2214.793.0793ceffective6f84vomit , diarrhoea , anuria341.923.7230.0534.0706feffective7m88vomit , oliguria , fever1342.695.9623.7420.0815pdeffective8m77anuria241.618.1249.0908.0635pdcure9m66anuria , fever341.585.6827.5448.31,108pdeffective10m106oliguria20.995.6716.1164.8833ceffective11m2020vomit , anuria , abdominal distention121.795.7339.7711.0647ceffective12f80.5anuria1342.225.5724.7575.91257pdeffective13m77oliguria , abdominal distention2340.345.7821.0248.8820fcure14m1717anuria341.142.9418.0181.5952ceffective15m77diarrhoea , haematuria , oliguria140.775.1022.4387.4830pd + ceffective16m1313diarrhoea , vomit , anuria121.125.4223.5381.01,247feffective17m77anuria12341.786.4825.6375.0614pdcure18f88diarrhoea , oliguria1242.586.3430.5854.0993pd + ccure19m2212anuria , fever2340.954.4626.8670.9940pdeffective20f106vomit , oliguria , fever44.8619.5157.0195feffective21m127anuria141.215.5921.0290.0709feffective22m3624anorexia , oliguria240.424.9427.7439.0439hdcure23f1111haematuria , oliguria1242.608.8447.3598.0621ceffective24f1111dysuria241.355.5719.1166.1442fcure25m82anorexia , oliguria10.104.5321.3194.3769fcurestone position : 1 . pelvis and calyces renalestreatment : c cystoscopy and retrograde catheterisation ; pd peritoneal dialysis ; hd haemodialysis ; f fluid administration specific data on each of the 25 infants hospitalised for melamine - induced kidney stones complicated by acute obstructive renal failure stone position : 1 . ureter attaching to the bladder ; 4 . pelvis and calyces renales treatment : c cystoscopy and retrograde catheterisation ; pd peritoneal dialysis ; hd haemodialysis ; f fluid administration 3 ) were detected in all the calculi in a molar ratio of 1 : 1.2 to 1 : 2.1 . 3total ion chromatography of high - performance liquid chromatography  mass spectrometry ( lcms ) and mass spectrogram of uric acid ( detected in negative ion mode ) total ion chromatography of high - performance liquid chromatography  mass spectrometry ( lcms ) and mass spectrogram of uric acid ( detected in negative ion mode ) children with acute obstructive renal failure and oliguria for at least 2  days or anuria for at least 1  day were dialysed until clinical their chemistry parameters returned to reference ranges . surgical interventions to remove the stones were given to the patients with severe hydronephrosis and to the anuric patients in whom dialysis was ineffective or unsuitable . in our study , 11 patients ( 44% ) underwent cystoscopy and retrograde catheterisation ; seven ( 28% ) patients were dialysed , of whom six received peritoneal dialysis and one was haemodialysed ; and the remaining seven patients ( 28% ) received only fluid administration for 4 to 20  days . the solutions of 11.4% sodium bicarbonate were administered intravenously once or twice daily at a dose of 2  ml / kg to these patients and they were encouraged to drink plain water . their urine ph values were continuously monitored for them to reach 6.57.0 . before fluid administration , the stone sizes ranged from 0.10 to 1.92  cm ( by ultrasound ) , but after alkalisation , they reduced to 0 to 1.72  cm . the renal functions returned to normal within 7  days ( median 3  days ) in all of the patients . creatinine concentrations decreased to normal concentrations in 3.5    1.89  days in the cystoscopy group , in 3.8    2.26  days in the dialysis group and in 2.7    1.60  days in the patients receiving fluids . according to the criteria we mentioned earlier in this article , six of the 25 patients were cured and 19 were effective by the time of discharging . twenty - two patients were reviewed from may 1st 2008 to september 5th 2009 ; three patients failed the follow - up because of changes of address . at follow - up visits , all of the 22 patients had normal renal function and normal urine routine . with ultrasonography study , 68% of the patients were found to have no urinary tract calculi at 3  months follow - up , 90% at 6  months and to the two patients who still had calculi after 6  months , potassium sodium hydrogen citrate granules ( 1  g / day , oral ) was given . after that , one patient had no stones at 8  months and the other had his calculi decreased in size . the latter was an 8-month - old boy with the largest stone ( 2.69  cm ) . eleven months after discharge from our hospital , the size of the stone was still quite big ( 1.20  cm ) , then , ultrasound - guided extracorporeal shockwave lithotripsy was given to this patient successfully . till now ( 15  months follow - up ) , no stones were found by urinary tract ultrasonography , and the urinalysis and renal function of the patient remained normal . 4follow - up of 22 of the patients follow - up of 22 of the patients physicians should take into consideration obstructive nephropathy when infants show clinical signs of pain , vomiting , haematuria and the presence of crystals during a urinalysis . the diagnostic approach for infants with suspected melamine - induced kidney stones relies heavily on ultrasonography of the urinary tract because melamine - uric acid calculi can not be detected by radiography . calculi or crystals have to be at least 1  mm in diameter in order to be detected by ultrasonography . intravenous pyelography ( ivp ) , in which calculi manifest as filling defects , may also be used to evaluate renal function , although this technique was not used in these 25 patients . computerised tomography ( ct ) did not provide definite evidence for diagnosis , so is not recommended . accurate diagnosis is the key to successful treatment and outcome , and must include detailed feeding history , clinical examination , imaging data and chemical analysis of urine and calculi . this is in agreement with the ratio reported in a study assessing the influence of gender on the development of paediatric renal stones . the anatomical features of the male urethra are different from females in terms of length , stegnosis and arcuations ; these differences may predispose male infants to urinary tract calculi because of the larger difficulty in passing stones . this study demonstrates that no cyanuric acid contributed to the calculus formation in the affected infants and that the calculi consisted of both uric acid and melamine . we postulate that melamine is alkalescent and some forms of melamine can turn into cyanuric acid while contacting strong acid in gastric juice , and cyanuric acid can then lower body fluid ph values . when ph values are lower than 5.5 , uric acid tends to accumulate and form crystals that can block urine flow in the tubules [ 2 , 4 , 13 ] . the renal failure results from both intrarenal crystal - associated obstruction and an elevation in renal pressure that reduces renal blood flow and glomerular filtration . it is a mechanical obstruction that results in renal damage , rather than a systemic toxic effect [ 5 , 710 ] . as urinary ph played an important role in the development of melamine - uric acid calculus , urine alkalisation with potassium citrate or sodium bicarbonate in our treatment proved to be highly effective , resulting in dissolution of the existing stones [ 6 , 11 ] . twelve to seventeen months follow - up demonstrated that most of the patients passed all stones within 3  months . when it is difficult to expel stones after 6  months , surgical intervention should be considered to help the patient to get rid of the stones which are large in size ( e.g. 1  cm ) or located at poor positions , e.g. renal pelvis and calyces renales . one of the 25 patients who did not expel all the stones after 11  months was given ultrasound - guided extracorporeal shockwave lithotripsy and the patient was cured without any complications . currently , a further follow - up survey for the 25 patients is being carried out by our hospital . in conclusion , melamine - contaminated formula can cause urinary system calculi and acute obstructive renal failure in infants . the stones are composed of uric acid and melamine at a molar ratio ranging from 1.2:1 to 2.1:1 , without evidence of the presence of cyanuric acid or other melamine analogues . therapeutic interventions have included oral fluid ( plain water ) administration , intravenous fluid administration and alkalisation of urine ( to reach urine ph values of 6.57.0 ) with bicarbonate . peritoneal dialysis , haemodialysis and surgical intervention for the removal of the stones were necessary in treating severe cases . the 12 to 17  months follow - up revealed no sequelae , while the long - term prognosis is still unclear and needs further observations .
a total of 25 chinese patients aged 6 to 36  months hospitalised at beijing children s hospital due to melamine - induced kidney stones complicated by acute obstructive renal failure in 2008 were included in a study in order to diagnose and treat these special cases more effectively . 
 feeding history , clinical presentation , ultrasound findings , treatments and effects were summarised . 
 twelve to seventeen months follow - up was reported also . 
 ultrasound examination showed that calculi were located at the kidney and ureters . 
 stones were composed of both uric acid and melamine in a molar ratio of 1.2:1 to 2.1:1 . 
 treatments providing liquid plus alkalisation of urine proved to be effective in helping the patients pass the stones . 
 surgical intervention was needed in severe cases . 
 renal function returned to normal in all 25 patients after various durations of therapy . 
 sixty - eight percent of the patients expelled all of the calculi within 3  months , 90% in 6  months and 95% in 9  months , without sequelae till now . 
 melamine - contaminated milk formula can cause kidney stones in infants , which should be diagnosed by feeding history , clinical symptoms and ultrasound examination . 
 composition of the stones was not only of melamine but also uric acid . providing liquid orally or intravenously plus alkalisation of urine proved to promote the removal of the stones . 
 follow - up of 12 to 17  months after discharge showed no sequelae .