urinary stone disease , or urolithiasis , is one of the most common afflictions of modern society.1 it is a common urologic disease with prevalence of about 1%20% that is increasing throughout the world .
urinary stone incidence in iran is high.2,3 the highest incidence was reported in ilam province , western iran , at 3222 per 100,000 people per year.4 the incidence in qom province is 234 per 100,000 people per year.4 urinary stone analysis is important in determining the possible etiology and pathophysiology of stone formation .
a better understanding of stone composition may help prevent urinary stone formation.5 incidence and composition of urinary stones has wide geographic variation .
people believe that the quality of water supply and its mineral content , specifically calcium , may contribute to urinary stone formation.6 mineral content of tap water differs dramatically throughout iran depending on the water source .
qom province , located in central iran s desert , has a hot and dry environment , which may influence the prevalence or quality of stone formation . in this prospective study ,
the prevalence of different biochemical forms of urinary stones was analyzed and its relationship with tap water hardness was evaluated .
from march 2008 to july 2011 all stones retrieved from patients with renal or ureteral stones were sent for biochemical analysis . to rule out the effects of infravesical obstruction , bladder stone cases were excluded .
analysis was performed in two nonprofit private medical laboratories ( boo - ali and danesh medical laboratory ) .
gender and age of patients , water source , and composition of stones were analyzed .
stones were obtained by spontaneous passage , surgical manipulation ( open or endoscopic surgery ) , or after extracorporeal shockwave lithotripsy .
included patients were residents of qom for at least 5 years , and all consumed city tap water as drinking or cooking water .
each stone sample was washed , dried , and crushed and then analysis was performed using semiquantative chemical analysis technique ( merckognost urinary analysis kit ; merck , darmstadt , germany ) .
there were 255 patients included in the analysis , 212 were males ( 83% ) and 43 were females ( 17% ) aged 14 to 84 years .
all of the stones except one were mixed calculi , evidenced by major and minor stone components .
the most frequent major component of stones was calcium oxalate ( 73% ) , followed by uric acid ( 24% ) , ammonium urate ( 2% ) , and cystine ( 1% ) .
table 3 and table 4 show the sex distribution of calculi patients based on the major and minor component of stones , respectively .
the mean age of calculi patients was 42.4 years ( median 45 years , standard deviation 11.87 years ) .
hardness range is 3901202 ppm with a mean of 651 ppm.7 its tap water ranks number one among iran s 28 provinces for hardness .
water hardness is defined as the molar sum of calcium and magnesium found in water.4,8 on the basis of water quality association classification , water hardness data were classified into five groups : soft ( < 17.1 ppm ) , slightly hard ( 17.160 ppm ) , moderately hard ( 60120 ppm ) , hard ( 120180 ppm ) , and very hard ( > 180 ppm).9 with a daily water intake of 2 l , inhabitants in areas with very hard water receive at least 360 mg of calcium daily ( 30% of reference value).4 the quality of qom province tap water is very hard ( 443.7 ; table 6 ) . in recent years , the use of treated home water by miniature house desalination plants has become very common .
comparing the results of this study with those from previous studies,1012 no significant difference ( p > 0.05 ) in biochemical stone analysis distribution between qom province and other provinces with softer drinking water was found .
calcium oxalate stones were present as calcium oxalate dihydrate ( weddelite ) or monohydrate ( whewellite ) . these calcium oxalate stone subtypes were not evaluated in this study .
mehrsai et al10 evaluated urinary calculi in two large urban areas of iran with much softer drinking water and found that the most common stone type was weddelite , seen in 77% of mixed stones . in another similar iranian study of 103 stones , the most common component was whewellite ( 81.5%).12 in sun et als13 study of 177 urinary stones , whewellite ( 50% ) and weddelite ( 15% ) were found to be the most common stone .
similar to the results in this current study , another study from iran showed that the most common component of stone in 165 pediatric urolithiasis cases was calcium oxalate.11 the facilitative role or protective role of water hardness in stone formation is controversial and still to be proven.1416 although the lithogenic effects of water hardness is not proven , it has been shown in some studies that the calcium quantity of tap water may cause hypercalciuria with concomitant hypooxaluria.14,17 bellizi et al18 observed that drinking soft water is preferable to hard water , as it is associated with a lower risk of calcium stone recurrence .
in contrast , sierakowski et al19 found that living in areas with a hard water supply is related to less urolithiasis formation .
on the basis of this study , there is no relationship between the quality of tap water and the distribution pattern of urinary stones .
although there is a conflict between water hardness and incidence of urinary stone formation , no correlation was found between water hardness and the type of urinary stones in qom province .
 purposethe aim of this study was to evaluate the biochemical stone composition in general population of qom province , central iran , and its relationship with high tap water hardness.materials and methodsin a prospective study , from march 2008 to july 2011 , biochemical analysis of urinary stones in patients living in qom province for at least 5 years was performed . 
 stones were retrieved by spontaneous passage , endoscopic or open surgery , and after extracorporeal shockwave lithotripsy . 
 demographic findings and the drinking water supply of patients were evaluated and compared with biochemical stone analysis.resultsstone analysis was performed in 255 patients . 
 the most dominant composition of urinary stones was calcium oxalate ( 73% ) , followed by uric acid ( 24% ) , ammonium urate ( 2% ) , and cystine ( 1% ) . 
 the peak incidence of urinary stone was in patients in their forties . 
 overall male to female ratio was 4.93:1.conclusionthe dominant stone composition in inhabitants of central iran , where tap water hardness is high , was calcium oxalate stones . 
 on the basis of this study , biochemical urinary stone composition of qom does not differ from other regions of iran with lower water hardness . 
Introduction
Materials and methods
Results
Discussion
Conclusion