Evaluation of chemical composition of urinary calculi by conventional radiography

BACKGROUND AND PURPOSE: The choice of the most efficient treatment modality for renal calculi could be facilitated by determining the precise chemical stone composition before treatment. We investigated the possibility of using conventional X-ray imaging to determine stone composition and to find a simple method of predicting stone fragility for treatment planning. MATERIALS AND METHODS: The X-ray density of 92 stones with known infrared spectroscopy analyses (calcium oxalate monohydrate, calcium oxalate dihydrate, struvite, and calcium phosphate) was retrospectively investigated by scanning the films with a digital camera. The data analysis was done using a commercially available graphics program to compare the total gray-scale levels of the stones. RESULTS: There was a significant difference in the mean gray-scale level of calcium phosphate and calcium oxalate stones (P < 0.01). The mean gray-scale difference between calcium oxalate dihydrate and calcium oxalate monohydrate was also significant (p < 0.02). All calcium oxalate, struvite, and calcium phosphate stones were correctly identified. Of the calcium oxalate monohydrate and calcium oxalate dihydrate stones, 98.4% and 66.6%, respectively, were correctly identified. CONCLUSION: The method allows a reliable diagnosis of stone composition from radiographs, which can be useful in stone treatment planning.     

Calcium stone disease: a multiform reality

In calcium renal stones, calcium oxalate and calcium phosphate in various crystal forms and states of hydration can be identified. Calcium oxalate monohydrate (COM) or whewellite and calcium oxalate dihydrate (COD) or weddellite are the commonest constituents of calcium stones. Calcium oxalate stones may be pure or mixed, usually with calcium phosphate or sometimes with uric acid or ammonium urate. The aim of this study was to compare the clinical and urinary patterns of patients forming calcium stones of different composition according to infrared spectroscopic analysis in order to obtain an insight into their etiology. The stones of 84 consecutive calcium renal stone formers were examined by infrared spectroscopy. In each patient, a blood sample was drawn and analysed for serum biochemistry and a 24-h urine sample was collected and analysed for calcium, phosphate, oxalate, citrate and other electrolytes. We classified 49 patients as calcium oxalate monohydrate (COM) stone formers, 32 as calcium oxalate dihydrate (COD) stone formers and three as apatite stone formers according to the main component of their stones. Patients with COM stones were significantly older than patients with COD stones (P<0.002). Mean daily urinary calcium and urinary saturation with respect to calcium oxalate were significantly lower in patients with COM than in those with COD stones (P<0.000). Patients with calcium oxalate stones containing a urate component (10%) presented with higher saturation (P<0.012) with respect to uric acid in their urine (and lower with respect to calcium oxalate and calcium phosphate, respectively P<0.024 and P<0.003) in comparison with patients without a urate component in the stone. Patients with calcium oxalate stones with a calcium phosphate component (15%) showed higher (P<0.0016) urinary saturation levels with respect to calcium phosphate (and lower with respect to uric acid (P<0.009), compared with patients forming stones without calcium phosphate or with a low calcium phosphate component. Patients with calcium stones mixed with urate had a significantly lower urinary pH (P<0.002) and urinary calcium (P<0.000), and patients with calcium phosphate >15%, higher urinary pH (P<0.004) and urinary calcium (P<0.000). In conclusion, in the evaluation of the individual stone patient, an accurate analysis of the stone showing its exact composition and the eventual presence of minor components of the stone is mandatory in order to plan the correct prophylactic treatment. Patients with calcium stones could require various approaches dependent on the form and hydration of the calcium crystals in their stones, and on the presence of minor crystalline components that could have acted as epitaxial factors.     

Stone composition and metabolic status

This paper aims to study the correlation between biochemical risk factors of the stone former and the type of oxalate stone formed, namely calcium oxalate monohydrate (COM) and calcium oxalate dehydrate (COD). A retrospective study of 487 patients who had been attending the urinary stone clinic, Trivandrum during 1998–2007 was conducted. The stones retrieved from them were subjected to chemical analysis and FTIR spectrographic analysis. They were categorized into COM, COD, mixed COM+COD and others. Of 142 pure calcium oxalate stone patients, 87 were predominantly COM stone formers and 55 COD stone formers. Their metabolic status of 24 h urine and serum was assessed. The values of urine calcium, phosphorus, uric acid, magnesium, creatinine, oxalate, citric acid, sodium and potassium, serum values of calcium, phosphorus, uric acid, magnesium and creatinine and calculated values of creatinine clearance, tubular reabsorption of phosphate, calcium magnesium ratio and calcium oxalate ratio were recorded. Comparison was made between the COM stone group and the COD stone group. Patients forming COM stones had significantly higher mean values for urine calcium (P < 0.05), oxalate (P < 0.01) and magnesium (P < 0.05) levels and significantly lower level of urine calcium–oxalate ratio (P < 0.01) and urine calcium–magnesium ratio (P < 0.01) compared to COD stone forming patients. All other values failed to show significant difference. Patients, with higher urine oxalate, formed COM stones. Those with low magnesium (which is an inhibitor) formed more of COD stones. Urine calcium was high in both groups without showing significant variation from the mean. In patients with high calcium–oxalate and calcium–magnesium ratios, there is higher chance of forming a COD stone than COM. Identification of the crystallization pattern of the calcium stone will help in selecting treatment modalities.     

Stone fragility: its therapeutic implications in shock wave lithotripsy of upper urinary tract stones

OBJECTIVE: To analyse the impact of stone composition on stone fragility (fragmentation) and clearance of upper urinary tract stones after shock wave lithotripsy (SWL). MATERIAL AND METHODS: Between 1st July 1998 and 31st July 2001, 300 renal and ureteric units of 290 patients (10 being bilateral) underwent SWL for upper urinary tract calculi. The degree of fragmentation was divided into four types: (I) Excellent, (II) Good, (III) Fair and (IV) No fragmentation. Stone composition was done by X-ray diffraction crystallography. A statistical comparison was made between degree of fragmentation, number of shock waves delivered, voltage setting, number of sessions required and requirements of adjuvant procedures according to the stone composition. RESULTS: Stone analysis revealed that 90% of the patients had calcium oxalate stones. Of these 80% were calcium oxalate monohydrate (COM) and 20% calcium oxalate dehydrate (COD). Struvite, apatite and uric acid stones comprised of 6%, 3% and 1% respectively. Type-I fragmentation was achieved up to 63.96%, 50% and 100% in COD, struvite and uric stones respectively as compared to 44.9% and 44.44% for COM and apatite stones. Type-III fragmentation was seen up to 8.79% and 33.3% respectively in COM and apatite as compared to 5.55% or less in other types of the stones suggesting that COM and apatite stones produce larger fragments. The mean number of shock waves, voltage and number of treatments was significantly higher for COM and apatite stones (p value < 0.005) with a stone free rate of only 65-66% and 65-68% respectively at three months (p value < 0.001). Similarly the number of adjuvant procedures required in COM alone was more, i.e. 31 as compared to 17 procedures in rest of the other kinds of stones (p value < 0.05). CONCLUSION: Stone composition in Indian subcontinent is different from the western world. Fragility of a stone varies with the composition of the stone and affects the therapeutic results.     

Morphology of urinary stone particles resulting from ESWL treatment

Fragments of urinary stones resulting from extracorporeal shock wave lithotripsy were examined by light and scanning electron microscopy. Calcium oxalate monohydrate and uric acid stone fragments were homogeneous and regular whereas struvite stone fragments were irregular in shape. Examination of the fractured surfaces revealed that the process of stone fragmentation involved fracture and cleavage of the crystals at some places and their separation from each other at others. In stones whose crystals are organised in layers, for instance calcium oxalate monohydrate and uric acid, crystalline layers separated along the concentric laminations. In struvite stones, which are an agglomeration of struvite and calcium phosphate crystals, major fragmentation occurred along the crystalline interfaces.     

复杂性肾结石化学成分分析(附84例报告)

目的 :分析复杂性肾结石化学成分特点 ,为预防其复发提供依据。方法 :对 84例在我院行微经皮肾镜取石术的复杂性肾结石患者 (纳入标准为鹿角形结石、单肾或双肾多发性结石且最大结石直径 >2 .5cm)进行结石化学成分分析 ,同时收集相关临床资料。结果 :80例 (95 .2 % )为含钙混合性结石和感染结石 ,其中草酸钙加磷酸钙 30例 (35 .7% ) ;草酸钙加尿酸 14例 (16 .7% ) ;草酸钙加磷酸钙加尿酸 10例 (11.9% ) ,草酸钙加磷酸钙加胱氮酸 1例 ;含钙结石并发感染结石 14例 (16 .7% ) ;感染结石 11例 (13.1% )。 4例 (4 .8% )为单一成分。结论 :体积较大的复杂性肾结石成分复杂 ,生长过程中常多种病因参与 ,应加强其病因诊断和针对多种病因采用积极的预防性治疗     

尿液成分对草酸钙结石的影响

目的 探讨尿液成分对草酸钙尿结石形成的影响。方珐 应用红外光谱仪对50份尿结石标本进行成分检测；对16例一水草酸钙（COM）与10例二水草酸钙（COD）尿结石患者的24h尿液进行生化检测，并比较两组生化指标。结果 87．5％的c0M结石患者和90％的c0D结石患者24h尿量减少；COM结石患者尿钙（4．94±2．11）mmol／24h，COD结石患者尿钙（9．43±3．78）mmol／24h；差异有统计学意义（P〈0．01）；COM结石患者尿磷（20．50±8．76）mmol／24h，COD结石患者尿磷（28．38±10．21）mmol／24h，差异有统计学意义（P〈0．05）；87．5％的COM结石患者尿枸橼酸低于正常水平。结论 COD结石患者尿钙、尿磷高于COM结石患者，表明COD结石的形成与高钙尿和高磷尿有关；COM结石的形成可能与低尿枸橼酸有关。     

Stone fragility--a new therapeutic distinction

The ESWL retreatment rates for calculi of 1.1 to 3.0 cm. varied according to stone composition: calcium oxalate monohydrate (COM) 10.3%, calcium oxalate dihydrate (COD) 2.8%, struvite/apatite calculi 6.4%. Fine detail in-vitro radiographs of approximately equal sized calculi composed of COM, COD, struvite, brushite, uric acid and cystine showed structural differences which may account for differences in their fragility. The same six calculi were fragmented in vitro in the Dornier HM3 lithotriptor by 200 shocks at 18 KV and the percent weight of each calculus able to be filtered through a two mm. sieve was determined; COD and uric acid (100%); COM (64%); struvite (57%); brushite (47%); cystine (16%). The linear density of these calculi, measured by single photon emission absorbtiometry, correlated with radio-density, not fragility. Calculi of varying composition respond differently to shock wave fragmentation. The assessment of the capability of ESWL to fragment a stone will determine the size stone selected for treatment. Therefore, "stone fragility" is a new distinction which deserves to be included in the conversation about urinary calculi.     

Determination of the chemical composition of urinary calculi by noncontrast spiral computerized tomography

Various techniques for noncontrast spiral computerized tomography (NCCT) were utilized for the determination of the Hounsefield unit (HU) values of various types of urinary calculi with the aim of determining the best technique for distinguishing various stones compositions. A total of 130 urinary stones, obtained from patients who underwent open surgery, were scanned with a multidetector row scanner using 1.25 mm collimation at two energy levels of 100 and 120 kV at 240 mA. Two post-scanning protocols were used for the HU value assignment, tissue and bone windows, for both kV values. In both protocols, three transverse planes were defined in each stone, one near the top, one in the middle, and one near the bottom. Three regions of interest (ROI) were obtained in each plane. The absolute HU value was determined by three methods: the mean of the nine ROI, the mean of the central three ROI, and the central ROI in the middle plane. Determination of the stones composition was performed using the absolute HU value measured at 120 kV, the dual CT values (HU values at 100 kV–HU values at 120 kV), and HU values/stone volume ratio (HU density). All stones were analyzed by x-ray diffraction to determine their chemical composition. After the exclusion of groups with few calculi, 47 pure stones [25 uric acid (UA), 15 calcium oxalate monohydrate (COM), seven struvite], and 60 mixed stones [15 COM 60–90%+hydroxyl apatite (HA), 14 COM 40–90%+UA, 21 UA+COM <40%, ten mixed struvite+COM+hydroxyl apatite] were included in the statistical analysis. From the least to the most dense, the pure stone types were UA, struvite, COM. Mixed UA+COM<40% calculi were less dense but insignificantly different from pure UA, while when the COM ratio was 40% their density became higher than and significantly different from pure UA, and less than but not significantly differentiated from pure COM. Mixed COM+HA were the most dense stones. Using the absolute HU values at 120 kV and HU density, we could distinguish, with statistical significance, all pure types from each other, pure UA from all mixed calculi except UA+COM <40%, pure COM from mixed UA+COM <40%, and pure struvite from all mixed stones except mixed struvite stones. Dual CT values were not as good as absolute HU values and HU density in the determination of stone composition. These results demonstrate that absolute HU values and HU density derived from CT scanning using a small collimation size could uncover statistically significant differences among all pure and most of the mixed urinary stones. This permits more accuracy in the prediction of stone composition. Moreover, this technique permits diagnostic conclusions on the basis of single CT evaluation.     

Conversion of calcium oxalate to calcium phosphate with recurrent stone episodes

PURPOSE: We have extended our previous observation that the percent occurrence of calcium oxalate stones decreased while that of calcium phosphate stones increased with each new stone event. MATERIALS AND METHODS: The National VA Crystal Identification Center has analyzed veteran patient urinary tract stones from VA hospitals throughout the United States since 1983. We reviewed the composition of 33,198 stones with emphasis on the changes in composition. More than 11,786 stones came from 5,088 recurrent stone formers. Stones were analyzed using high resolution x-ray powder diffraction and Fourier transform infrared spectroscopic techniques. When the stones were investigated as a function of time, it was determined that there was greater variability when samples were more than 30 days apart. RESULTS: The percent occurrence of whewellite, weddelite, apatite, brushite and uric acid in stones increased between 1.0% and 5.9% since our previous study. The percent occurrence of struvite decreased by 2.6%. The percent of calcium oxalate stones decreased while that of calcium phosphate stones increased with each new event. However, the total percent occurrence of all calcium containing stones did not significantly change with recurrent stone events. CONCLUSIONS: Our study suggests a strong trend for the conversion of stone disease from calcium oxalate to calcium phosphate containing stones, which could influence the progression and severity of disease.     

Some data on urinary stones which were passed.

Out of a group of 979 patients with urinary calculi, 175 had passed their stone(s). Comparison of data for stones which had been passed with data for the whole group shows many significant differences. Calculi composed entirely of calcium oxalate are more likely to be expelled than any other composition variety. The chance of this happening is 1 in 3 and it is even higher when the person is under 50 years of age. The probability of calculi composed of calcium oxalate+calcium phosphate being expelled is 1 in 5 and this also increases for younger patients. Infection stones consisting of calcium phosphate+struvite have only 1 in 19 chance of being passed. Many of the stones passed (130) are under 0.10 g in weight. However, there is a similar relationshp between composition and weight among both the stones that were passed and the whole group. In both groups, pure oxalate stones are the lightest, infection stones are the heaviest and stones composed of calcium phosphate and calcium phosphate+calcium oxalate are of intermediate weight.     

Calcium oxalate monohydrate binding protein: a diagnostic biomarker for calcium oxalate kidney stone formers

Urinary oxalate is a biomarker for calcium oxalate kidney stone disease; however, its assay is insensitive and nonspecific. Calcium oxalate monohydrate (COM) binding protein (45 kDa) is a promoter of calcium oxalate kidney disease, which is markedly upregulated by oxalate induced oxidative stress. The current study was carried out to evaluate whether COM binding protein can serve as a diagnostic marker for calcium oxalate kidney stone formers. COM binding protein was isolated, purified and antibody was raised against it in rabbits. Urine samples (24 h) were collected from patients suffering from various kidney diseases such as acute nephritis, chronic nephritis, nephrotic syndrome, calcium oxalate (CaOx) stone formers, uric acid stone formers, struvite stone formers and calcium phosphate stone formers. This COM binding protein was quantified by an in house ELISA method and the excretion was found to lie between 2 and 3 mg in control samples, while in CaOx stone formers it was detected between 11 and 19 mg. Urinary risk factors were assayed. We conclude that COM binding protein can serve as a diagnostic marker for CaOx stone formers.     

Reduced glomerular filtration rate and hypercalciuria in primary struvite nephrolithiasis

Struvite nephrolithiasis is caused by infection with bacteria that possess the enzyme urease, and convert urea to ammonia that raises urine pH and crystallizes with magnesium and trivalent phosphate ion. Of the 75 of our 1431 stone patients with struvite stones 52 were women. Struvite stones occurred almost exclusively in women; a minority of women and most men had mixed stones of struvite and calcium oxalate. Increased serum creatinine levels and reduced creatinine clearance were common in patients with struvite stones, not in those with mixed stones; both were rare in calcium stone disease. Men and women with mixed struvite, calcium oxalate stones were hypercalciuric, but women with struvite stones were not. Patients with mixed stones usually had initial symptoms of stone passage, and were less likely to need surgery, including nephrectomy, or to form contralateral stones. Patients with struvite stones usually presented with infection or no symptom, not passage. We conclude that struvite stones occur in two forms. The struvite stone is a disease of women, presumably occurring de novo from infection. The mixed stones occur in both sexes, presumably from secondary infection in hypercalciuric patients who begin with calcium-oxalate stone disease.     

Prevention of stone disease

In recent years stone disease has become more widespread in developed countries. At present the prevalence is 5.2 and 15% of men and 6% of women are affected. The increase is linked to changes in lifestyle, eating patterns and obesity which has become very common. The 'metabolic syndrome' includes all the diseases, e.g. hypertension, lipid imbalances, type 2 diabetes mellitus, gout and cardiovascular disease, which are concomitant in the majority of stone formers. Dietary patterns, besides leading to stone formation, also determine stone chemistry. With a diet that is rich in oxalates, calcium oxalate will constitute 75% of stones, struvite 10-20%, uric acid 5-6% and cystine 1%. As approximately 50% of patients with stones suffer recurrences, metabolic and/or pharmacological prophylaxis is recommended.     

Formation of the staghorn calculi

To study the process of formation of staghorn calculi, 58 patients with staghorn calculi were evaluated clinically and the removed stones were studied architecturally. Of 35 patients with infection stones composed of struvite and/or apatite in the nuclei as well as peripheral layers, 18 had identified predisposing factors related to infection. Of 13 patients with infection stones containing calcium oxalate in the nuclei, 7 had predisposing factors of infection but only 2 had metabolic disorders. The patients with infection stones who had no predisposing factors may have transient or subclinical abnormalities. Initial stone formation of oxalate may also be one of the predisposing factors of infection. Most of the patients with staghorn calculi composed of uric acid, oxalate and cystine, had metabolic disorders related to these substances. Large numbers of bacteria and large amounts of organic matrix were found extensively within infection stones and were thought to be important components as well as crystals. Metabolic stones contained little matrix. In this case crystal aggregation is thought to play the most important role in stone formation.     

Changes in stone composition according to age and gender of patients: a multivariate epidemiological approach

Urinary stone incidence and composition have changed markedly over the past half-century in industrialized countries, in parallel with profound changes in living standards and dietary habits, with a dramatic increase in the incidence of calcium oxalate stones. However, studies evaluating the influence of age and gender on the distribution of the various types of urinary calculi are scarce. We report the results of a study based on 27,980 calculi (from 19,442 males and 8,538 females) analyzed by infrared spectroscopy between 1976 and 2001. The relationships between age and sex and stone composition were investigated using a multivariate approach, based on correspondence factor analysis (CFA). We found a male predominance for calcium oxalate and uric acid, a female preponderance for calcium phosphate and struvite stones, and an increasing prevalence of uric acid stones with age in both genders. CFA was able to reconstruct in blind the age curve from stone composition. The first two axes of the multidimensional classification, which correspond to age, included 86.9% of the total variance, indicating that age was the main factor involved in stone type. Superimposition of age classes and stone components showed a strong relationship between age and whewellite, weddellite, brushite, carbapatite, octacalcium phosphate and uric acid, while other substances (whitlockite, amorphous carbonated calcium phosphate, struvite, proteins, mucopolysaccharides, triglycerides or ammonium urate) appeared weakly related to age. In addition, CFA suggests the role of common lithogenic factors between weddellite, carbapatite and brushite, which clustered in the same area, whereas the various crystalline forms of phosphate stones segregated into two different clusters, suggesting distinct pathogenic factors. In conclusion, this study provides a picture of the present epidemiology of urinary stones in France. CFA helped to confirm: (1) an etiopathogenic distinction between weddellite and whewellite, (2) etiopathogenic associations between chemical compounds, which were only suspected on a clinical basis, and (3) suggested yet unrecognized associations, especially with respect to the heterogeneous group of phosphate stones.     

Carbonate in Struvite Stone Detected in Raman Spectra Compared with Infrared Spectra and X-Ray Diffraction

Background : In regard to identify the compositions of urinary stones, the infrared spectra is a contemporary routine method. However, it is difficult to detect the absorption of carbonate in struvite stone by infrared spectra, because NH₄ absorption of magnesium ammonium phosphate overlaps CO₃ absorption of carbonate at 1420–1435 cm^?1. With the purpose of demonstrating the existence of carbonate in struvite stones, the analysis of these stones by means of Raman spectra has been tried. Methods : Forty urinary stones, the chemical compositions of which were previously determined by infrared spectroscopy, were submitted to Raman spectrum analysis, and subsequently to analysis by x-ray diffraction. Results : Thirty of 40 urinary stones were found to be composed of struvite and of mixed struvite-calcium oxalate by infrared analysis. Twelve of these stones were shown to have Raman spectra of magnesium ammonium phosphate, and the other stones to have spectra of apatite. By x-ray diffraction magnesium ammonium phosphate crystals were detected in 25 of these struvite stones and hydroxyl-apatite in another 3, and 2 cases were undeterminable. For other components, such as calcium oxalate, uric acid and cystine, the analytical results of infrared spectra coincided with those of Raman spectra and x-ray diffraction. Carbonate was detected in only a part of one struvite stone by Raman spectra. Conclusions : Above-mentioned results may indicate that carbonate is only a minor component of urinary stones. Therefore, most of 1420–1435 cm^?1bands on the infrared spectra of struvite stones do not indicate CO₃ absorption of carbonate, but NH₄ absorption of magnesium ammonium phosphate.     

Results of urometabolic evaluation in 127 patients with renal calculous disease

One hundred twenty-seven selected stone formers were evaluated. With the simple ambulatory tests proposed by Pak for metabolic screening and a complete urologic evaluation an anomaly was found in more than 90 per cent of the cases. The patients were divided into three groups: (1) patients operated on for staghorn stones; (2) patients with episodes of spontaneous stone eliminations or young people with only one stone episode; and (3) patients operated on for stone disease. No significant differences were noted except for the occurrence of urinary tract infection and for struvite and calcium oxalate occurrence in the different groups. Urinary tract infection combined with a metabolic disorder appear to make the evolution from small kidney stone to staghorn stone a reality.     

Tensile,flexural and compressive strength studies on natural and artificial phosphate urinary stones

Mechanical properties of renal calculi dictate how a stone interacts and disintegrates by shock wave or intracorporeal lithotripsy techniques. Renal stones of different compositions have large variation in their mechanical strength and susceptibilities to shock waves. Operated urinary stones and artificially developed stones using pharmaceutical methods, composed of phosphates were subjected to tensile, flexural and compressive strength studies using universal testing machine. The infrared spectra confirmed the presence of hydroxyapatite in both the natural stones and struvite with calcium oxalate trihydrate in one stone and struvite with uric acid in the other. The X-ray diffraction analyses confirmed their crystalline nature. It has been observed that the flexural properties depend on the size of the sample even for the samples cut from a single stone. The compressive strengths were almost 25 times larger than the tensile strengths of the respective natural stones as well as the artificial stones prepared. This article directly relates to material presented at the 11th International Urolithiasis Symposium, Nice, 2–5 September 2008, from which the abstracts were published in the following issue of Urological Research: Urological Research (2008) 36:157–232. doi:.     

Characteristics of patients with staghorn calculi in our experience

PURPOSE: To elucidate the factors contributing to staghorn stone formation in patients. MATERIALS AND METHODS: The records of 82 patients (44 men and 38 women) with complete staghorn calculi were reviewed retrospectively for clinical presentation, metabolic disturbances and anatomical abnormalities. RESULTS: There were 79 unilateral and three bilateral cases. The patient performance of the activities of daily life was assessed with the modified Rankin scale (MRS) and it was found that 69 patients were functionally independent (84.1%, MRS 0-1) and 10 patients had a severe disability (12.2%, MRS 4-5). Seven patients had chronic indwelling catheters (8.5%). A positive urine culture was found in 24.4% of patients. Analysis of stone composition revealed magnesium ammonium phosphate and mixed calcium oxalate-phosphate were the most frequently identified types of stone (32.1% and 22.2%, respectively). Urinary pH was low in patients with uric acid stones (mean 5.4). Hyperuricemia, cystinuria and hypercalciuria were found in 14.6%, 2.4% and 37.8%, respectively. Hypercalciuria was found more frequently in calcium-stone cases. Eleven patients (13.4%) showed structural abnormalities of the kidney. CONCLUSIONS: Our data show that the patients with severe disability, urinary tract infection and hypercalciuria could be recognized more frequently in staghorn calculi compared with common urolithiasis. However, in Western countries, the frequency of both urinary tract infection and struvite stones is much higher than in our data. Other Japanese authors have also reported the low frequency of struvite stones in staghorn calculi, suggesting that various factors other than urinary tract infection possibly contribute to the formation of staghorn calculi in Japan.