Ammonium Acid Urate Research Articles

Dual-energy computed tomography for the differentiation of uric acid stones: ex vivo performance evaluation

We assessed the potential of dual-energy computed tomography (CT) for the differentiation between uric acid (UA)-containing and non-UA-containing urinary stones. Forty urinary stones of 16 different compositions in two sizes (<and>or=5 mm) were examined in an ex vivo model. Thirty stones consisted of pure calcium oxalate (whewellite or wheddellite), calcium phosphate (apatite, brushite, or vaterite), ammonium magnesium phosphate (struvite), UA, ammonium acid urate, ammonium phosphate, sodium hydrogen urate, or cystine, and ten stones were of mixed composition (UA-sodium hydrogen urate, whewellite-urate, wheddellite-urate, whewellite-brushite, or whewellite-brushite-struvite). Scans were performed using dual-source CT in a dual-energy mode with the tubes simultaneously operating at 80 and 140 kV. Two readers analysed the data with respect to stone attenuation at each energy level. The stones were classified as UA- or non-UA-containing using manual attenuation measurements and software analysis results. Sensitivity, specificity, PPV, and NPV were calculated using crystallographic stone analysis as the gold standard. Twenty-six out of 40 stones (65%) contained no UA; 14 stones (35%) contained UA. When compared with UA-containing stones, the differences in attenuation values at 80 and 140 kV were significantly (P<0.001) higher in stones containing no UA. The software automatically mapped 39/40 stones (98%). Only one (2%) 2 mm UA-stone was missed. The software correctly classified all detected stones as UA- or non-UA-containing. The attenuation values of the missed stone were manually plotted into the analysis sheet which allowed for the correct classification of the stone (containing UA). Therefore, the sensitivity, specificity, PPV, and NPV for the detection of UA-containing stones was 100%. Ex vivo experience indicates that differentiation between UA- and non-UA-containing stones can be accurately performed using dual-source dual-energy CT.

Analysis of Urinary Stone Components during the Last Two Decades

oxalate made up 73.1% of the total. Other components found in the stones were uric acid 12.3%, calcium phosphate 8.3%, magnesium ammonium 5.3%, ammonium acid urate 0.7% and cystine 0.3%. In Group B, calcium oxalate was only 56.3% of the total and uric acid was 22.2%, calcium phosphate was 11.4%, magnesium ammonium phosphate was 8.2%, ammonium acid urate was 1.3% and cystine was 0.6%. On comparison of the stones of the two groups, the incidence of calcium oxalate was decreased in Group A (73.1% vs 56.3%, p＜0.001). However, the incidence of uric acid in Group B was increased (12.3% vs 22.2%, respectively, p=0.006). There were no notable statistical increases in the frequency of the other components (p＞0.05). Conclusions: In this study, the incidence of calcium oxalate was decreased and that of the uric acid was increased in the recent decade. These changes of stone components probably resulted from the increased animal protein

Comparison of three techniques for the diagnosis of urinary tract infections in dogs with urolithiasis

To identify an appropriate sampling technique(s) to accurately detect the bacteria causing urinary tract infections in dogs with urolithiasis. Twenty-one dogs with urolithiasis were included in the study. Three types of samples were taken from each dog. Urine was collected by cystocentesis, and a urinary bladder mucosal biopsy and urolith were retrieved during cystotomy. The samples were then cultured on blood agar and MacConkey's agar to identify the bacteria associated with urinary tract infections. Bacterial urinary tract infection was found in 16 cases (76.19 per cent). The most prevalent bacteria found to cause urinary tract infection were Escherichia coli (n=7), followed by coagulase-positive Staphylococcus species (n=4), Klebsiella pneumoniae (n=2), Pseudomonas aeruginosa (n=2) and Proteus mirabilis (n=1). In the case of a positive urine culture, the same bacteria were also cultured from the urinary bladder mucosal biopsy alone or from both the urinary bladder mucosal biopsy and urolith. However, in the case of a negative urine culture, bacteria were found to be present in the urinary bladder mucosal biopsy or urolith cultures in 23.81 per cent of dogs. The uroliths that gave positive culture results were either infection-induced uroliths composed of struvite and calcium carbonate phosphate, ammonium acid urate only or metabolic uroliths composed of calcium oxalate and calcium phosphate, or calcium phosphate only. All the uroliths that gave negative culture results were metabolic uroliths composed of calcium oxalate and/or calcium phosphate, and uric acid and calcium phosphate. When the culture from the urine obtained by cystocentesis is negative, cultures of urinary bladder mucosal biopsy and urolith are recommended in dogs with urolithiasis in order to accurately assess the microbiological status of the urinary tract.

Ammonium acid urate urolithiasis in Japan

Ammonium acid urate (AAU) calculi are a rare urolithiasis in developed countries but are endemic in developing countries. We assessed the features of AAU urolithiasis in Japanese patients. We reviewed hospital charts of patients with urolithiasis who were treated with extracorporeal shock wave lithotripsy and endourological procedures at Sagamidai Hospital (Kanagawa, Japan) from January 1992 to December 2001. On the basis of the results of stone analysis with an infrared spectrophotometer, AAU stones were found. Of 8664 urolithiasis that we reviewed, 33 calculi (0.38%) from 29 patients contained AAU crystals. From crystallographic findings, we defined two types of AAU-containing stones: pure and mixed AAU urolithiasis. Pure AAU urolithiasis were seen in 13 stones from 10 patients and mixed AAU in 20 stones from 19 patients. We found significant differences between the groups: the pure AAU group predominantly consisted of young, thin women and the mixed group consisted of middle-aged men. Laboratory findings showed trends of low levels of serum protein, potassium, and urine pH in the pure AAU group. Because each type of AAU urolithiasis is associated with different patient characteristics and pathophysiological features, it is important to understand the type of AAU urolithiasis in patients with calculi.

The etiology of urolithiasis in HIV infected patients.

It is commonly thought that urinary lithiasis in HIV infected patients on protease inhibitor therapy is composed primarily of the protease inhibitor itself. Since many HIV infected patients on protease inhibitors presenting to our institution had nonprotease inhibitor stones, we investigated potential underlying metabolic abnormalities that may account for the lithogenesis. We retrospectively reviewed all HIV infected patients on protease inhibitors with renal colic and evidence of nephrolithiasis who presented to our institution between June 1996 and January 2001. Patients were evaluated for stone composition and metabolic abnormalities of blood and urine when possible. A total of 24 patients were identified, and all were or had been on protease inhibitors (indinavir 14, ritonavir 3, nelfnavir 2, unspecified 5). Of the 14 patients on indinavir only 4 (28.6%) had indinavir containing stones. The remaining stones in this group and in those not on indinavir contained various amounts of calcium oxalate monohydrate and dihydrate, ammonium acid urate and uric acid. Of 10 patients who underwent 24-hour urine collection for metabolic evaluation 8 (80%) had abnormalities, including hypocitraturia in 5, hyperoxaluria in 4, hypomagnesuria in 4, hypercalciuria in 3, increased supersaturation of calcium oxalate in 3 and hyperuricosuria in 2. Abnormalities in the levels of urinary phosphate and sodium were also observed. HIV infected patients form many types of stones, which probably are attributable to underlying metabolic abnormalities rather than the use of protease inhibitors. A complete metabolic evaluation is warranted in these patients, as a means of guiding treatment to prevent future stone episodes, while avoiding the need to alter antiretroviral regimens.

Kidney stone disease

About 5% of American women and 12% of men will develop a kidney stone at some time in their life, and prevalence has been rising in both sexes. Approximately 80% of stones are composed of calcium oxalate (CaOx) and calcium phosphate (CaP); 10% of struvite (magnesium ammonium phosphate produced during infection with bacteria that possess the enzyme urease), 9% of uric acid (UA); and the remaining 1% are composed of cystine or ammonium acid urate or are diagnosed as drug-related stones. Stones ultimately arise because of an unwanted phase change of these substances from liquid to solid state. Here we focus on the mechanisms of pathogenesis involved in CaOx, CaP, UA, and cystine stone formation, including recent developments in our understanding of related changes in human kidney tissue and of underlying genetic causes, in addition to current therapeutics.

Percutaneous cystolithotomy for pediatric endemic bladder stone: experience with 155 cases from 2 developing countries

Purpose The aim of this study was to evaluate retrospectively our experience with percutaneous cystolithotomy (PCCL) in children having endemic urinary bladder stones. Methods Between January 1993 and June 2003, 155 children younger than 14 years underwent PCCL. The patients' age ranged from 8 months to 14 years (average, 4.5 years). One hundred fifteen patients (74.2%) were 5 years or younger, 31 patients (20%) were between 6 and 10 years, and 9 patients (5.8%) were between 11 and 14 years. There were 153 boys and 2 girls. The stone size ranged from 0.7 to 4 (average, 2.3) cm. The procedure was done under general anesthesia. Dilation of the tract was made under fluoroscopy. The instrument was the adult 26F nephroscope, the same that is used for percutaneous nephrolithotomy. Ultrasound disintegration was needed for stones larger than 1 cm. Suprapubic catheter was left for 24 hours. Urethral catheter was kept for 48 hours. Results All patients became stone-free. The average operating time was 20 (5-60) minutes. The average hospital stay was 2.7 (2-5) days. No any severe intra- or postoperative complication was observed. The nucleus and/or the main component of the stones were ammonium acid urate in 144 patients (93%). Conclusions Based on our experience, we can conclude that PCCL is a safe and effective method for treatment of endemic bladder stones in children. It reduces morbidity and hospital stay, and thus the cost of treatment. Our series proves the nutritional etiology of the endemic pediatric bladder stones.

Renal stones in the tropics.

Urolithiasis is a problem that is generally increasing in the tropics as it is in most Western countries. There are 2 main types of the disorder-bladder stones in children, a form of the disorder that disappeared from Europe in the late 19th and early 20th centuries, and upper urinary tract stones in adults. The former has been decreasing in most countries in the so-called endemic bladder stone belt with gradual improvements in levels of nutrition. However, as living standards increase, particularly in the urban areas of the more affluent developing countries, so the incidence of upper urinary tract stones in adults is increasing. The types of stones formed depend mainly on the composition of urine, which, in turn, reflects the type of diet consumed in the countries concerned. The main factor that leads to the formation of bladder stones in children is a nutritionally poor diet that is low in animal protein, calcium, and phosphate, but high in cereal and is acidogenic. This leads to the formation of urine with a relatively high content of ammonium and urate ions and consequently to the formation of ammonium acid urate crystals and stones. In countries where there is also a high intake of oxalate from local leaves and vegetables, urinary oxalate is increased and, as a result, the ammonium acid urate stones often contain calcium oxalate as well. The stone problem in the tropics is compounded by low urine volumes resulting in some areas from poor drinking water, which causes chronic diarrhea, and in others from the hot climate and fluid losses through the skin. As nutrition improves in these countries, the formation of bladder stones gives way to upper urinary tract stones consisting of calcium oxalate, often mixed with calcium phosphate or uric acid, such as are formed in most Western countries.

Pediatric urolithiasis in Armenia: a study of 198 patients observed from 1991 to 1999.

To study prospectively the risk factors and etiology of urolithiasis in all stone patients aged <15 years admitted from 1991 to 1999 to the Arabkir hospital in Yerevan. Stones were obtained by surgery (64%), extracorporeal shockwave lithotripsy (ESWL) (7%) or cystoscopic extraction (4%); 25% passed spontaneously. All were examined by infrared spectroscopy, and spot urines were analyzed chemically. 198 patients, 180 (68% males) with renal stones and 18 (83% males) with primary bladder stones, were studied. Calcium oxalate (CaOx) was the predominant constituent in 62% of the kidney stones, followed by struvite (17%), calcium phosphate (7%), uric acid (7%), ammonium acid urate (5%), and cystine (2%). Bladder stones contained CaOx in 72%, uric acid in 22% and ammonium acid urate in 6% of patients. Etiology was obviously metabolic in 5% and possibly metabolic in 26%. Twenty percent of stones were infectious, and 19% were endemic (9% bladder and 10% kidney stones); 4% were secondary to urinary stasis with malformation but no infection. Etiology in 26% remained unknown. Stone composition and metabolic etiology are similar to that in central Europe and North America. In contrast, infectious calculi and particularly endemic stones are still common, although becoming less so now. Urolithiasis in Armenia thus reflects the transition from a rural to an urban society.

Percutaneous Suprapubic Cystolithotripsy for Pediatric Bladder Stones in a Developing Country

Objective: To evaluate our experience with percutaneous suprapubic cystolithotripsy (PCCL) in Yemeni children with endemic urinary bladder stones. Patients and Methods: Between January 1993 and December 1998, 117 children underwent percutaneous suprapubic lithotripsy in Arabia Felix Modern Hospital, Sana’a Republic of Yemen. The patients’ ages ranged from 8 months to 14 years (average 3.7 years). Ninety patients (77%) were under 5 years old; 20 patients (16%) were between 6 and 10 years old, and 7 patients (6%) were between 11 and 14 years old. There were 116 boys and 1 girl. The stone size ranged from 0.7 to 4 (average 2.3) cm. Five patients had coexisting urinary bilharziasis and another 5 patients had coexisting renal stone. In 10 patients, the stone was in the urethra. The procedure was done under general anesthesia. Dilation of the tract was made under fluoroscopy. The instrument was an adult 26–french nephroscope, the same as that used for percutaneous nephrolithotripsy. Ultrasound disintegration was needed for stones of >1 cm. A suprapubic catheter was left for 24 h, and a urethral catheter was kept for 48 h. Results: All patients became stone free. The average operating time was 15 (5–50) min. The average hospital stay was 2.7 (2–5) days. No severe intra– or postoperative complication was observed. The nucleus and/or the main component of the stones were ammonium acid urate in 109 patients (93%). Conclusion: Based on our experience we can conclude that percutaneous suprapubic lithotripsy is a safe and effective method for the treatment of bladder stones in children. It reduces morbidity and hospital stay and thus the cost of treatment. Our series proves the nutritional etiology of endemic pediatric bladder stones. To our knowledge, this is the largest series reported on percutaneous suprapubic management of endemic bladder stones in children.

CLINICAL USE OF CYSTINE SUPERSATURATION MEASUREMENTS

We measured the concentration and solubility of cystine in urine from patients with cystinuria or calcium stones and from normal subjects to determine whether urine cystine supersaturation can be calculated from a standard nomogram of solubility versus pH or needs to be measured directly. We also evaluated whether increasing pH of the 24-hour collection recovered enough crystallized cystine to increase cystine supersaturation. Cystine concentration, pH and usual stone risk factors were measured on 50 ml. aliquots of 24-hour collections from 24 patients with cystinuria, 22 calcium stone formers and 15 normal subjects. After 48 hours of incubation with sodium bicarbonate, a second aliquot was taken from the 24-hour collection for cystine concentration. The original urine at its ambient pH was incubated with an excess of cystine crystals for 24, 48, 72 or 96 hours at 37C to determine solubility and kinetics of equilibration. Cystine solubility varied so widely at any pH range that no predictive nomogram could be relied on for calculating supersaturation. Addition of sodium bicarbonate to the 24-hour urine significantly increased cystine concentration. Urine from stone formers had higher cystine solubility than urine from normal subjects. Clinical management of cystinuria can be improved by direct measurement of cystine solubility because it varies widely at any given pH. Increasing 24-hour collection pH with sodium bicarbonate additionally improves accuracy of supersaturation measurement by recovering crystallized cystine.

Relevance of sonographic artifacts observed during in vitro characterization of urocystolith mineral composition.

Nine pure mineral type canine uroliths (bladder or urethral origin only) were imaged ultrasonographically using 3.5 MHz, 5.0 MHz, and 7.5 MHz fixed focus, mechanical sector transducers in a urinary bladder phantom. The uroliths studied were those composed of 100% magnesium ammonium phosphate, calcium oxalate monohydrate, calcium oxalate dihydrate, calcium phosphate appatite, and calcium hydrogen phosphate dihydrate (brushite), ammonium acid urate, sodium acid urate, cystine, and silica. The occurrence of both reverberation/streak and acoustic shadowing artifacts were compared to urocystolith mineral type (classified by effective atomic number), urocystolith width, urocystolith height (thickness), and ultrasonographic imaging frequency. No predictable relationship was found between either of the artifacts seen beyond the urocystolith (reverberation/streak or the acoustic shadowing) and urocystolith mineral type. There was no statistical relationship between the occurrence of reverberation/streak artifact and the size (width or height) of the urocystolith or the ultrasonographic frequency. There was, however, a statistically relevant relationship between ultrasonographic imaging frequency and the occurrence of acoustic shadowing and between urocystolith height (thickness) and the occurrence of acoustic shadowing. However, regardless of ultrasound frequency, acoustic shadowing was observed less than 35% of the time in any of the urocystolith mineral types examined. Based on the imaging of the bladder phantom supporting apparatus (7.0 mm bolts covered by plastic), the accurate characterization of a curved object surface directly facing the transducer was found to be directly related to the frequency of sound used for imaging and at best predictably limited to curved vs flat. Accurate measurement of the maximum transverse dimension of an echogenic curved object or accurate characterization of the lateral borders of such an object was considered unlikely with general ultrasonographic equipment of the frequencies studied. Therefore, detailed architectural characterization of urocystoliths suitable for mineral composition prediction is considered highly unlikely with general pulse-echo ultrasonographic techniques.

Contrast medium-related artifacts observed during in vitro radiographic characterization of urocystolith mineral composition.

Nine pure mineral types of canine uroliths (bladder or urethral origin only) were exposed to sequential increasing concentrations of iodinated, radiographic contrast medium in petri dishes. The uroliths studied were those composed of 100% magnesium ammonium phosphate, calcium oxalate monohydrate, calcium oxalate dihydrate, calcium phosphate appatite, and calcium hydrogen phosphate dihydrate (Brushite), ammonium acid urate, sodium acid urate, cystine, and silica. Two phenomena were observed. First, there was a tendency for selected urocystoliths to undergo radiopacity augmentation beyond that expected for just contrast medium superimposition. This was termed, contrast medium adhesion, which persisted despite repeated washing of the urocystoliths. Second, there was a tendency for bubbles to form on or near selected urocystolith chemical types. These observations prompted careful scrutiny for their occurrence in subsequent clinical simulation of radiographic procedures using these same urocystoliths in a urinary bladder phantom. Imaging techniques simulated were survey radiography, pneumocystography, double contrast cystography (two iodine concentrations). The contrast medium adhesion occurrence found in the petri dish studies was compared to urocystolith mineral type. Similar comparisons were made for contrast medium adhesion occurrence in the bladder phantom. The detection of contrast medium adhesion in the bladder phantom differed from that observed in the petri dish experiments. While contrast adhesion occurred across a fairly broad range of the urocystolith mineral types in the petri dish studies, it was observed primarily for sodium acid urate and cystine urocystoliths in the bladder phantom. Prompted by the observation of bubbles in association with a limited number of urocystolith types in the petri dish studies, bubble occurrence in the bladder phantom was compared to the urocystolith type. Bubble formation on or near the urocystoliths, although uncommonly observed, was seen only with either cystine or silica urocystoliths. The potential clinical utility and clinical caveat aspects of these phenomena are discussed.

AMMONIUM ACID URATE CALCULI: A REEVALUATION OF RISK FACTORS

Purpose We reevaluate the demographic and metabolic risk factors for ammonium acid urate stones. Materials and Methods Since 1986, 23 women and 21 men ranging in age from 20 to 81 years (mean 48.7) were treated for stones partly composed of ammonium acid urate. Stone composition ranged from 2 to 60% ammonium acid urate (mean 24.1) of the total stone mass. No patient had a pure ammonium acid urate stone, although 11 (25%) had stones with ammonium acid urate as the predominant crystal. Results In the 44 patients 1 or more potential risk factors for ammonium acid urate were identified. Of the patients 11 (25%) had a history of inflammatory bowel disease with 10 (22.7%) having undergone ileostomy diversion, 6 (13.6%) admitted to a history of significant laxative use or abuse, 18 (40.9%) were morbidly obese, 16 (36.4%) had a history of recurrent urinary tract infections and 9 (20.5%) had a history of recurrent uric acid stones. Conclusions Patients clearly at risk for stones with an ammonium acid urate component include those with a history of inflammatory bowel disease and ileostomy diversion or laxative abuse. Other factors that may potentially enhance ammonium acid urate stone formation include morbid obesity, recurrent uric acid calculi and recurrent urinary tract infection. A careful history followed by further metabolic evaluation is warranted in these patients.

Ammonium acid urate crystal formation in adult North American stone-formers

Although ammonium acid urate (AAU) stones are endemic in Asia, pure AAU calculi have almost disappeared from industrialized countries and clinical pathophysiologic relevance of sporadic stones containing AAU crystals is currently unknown. We reviewed 1,396 crystallographic stone analyses performed in our institution over a 10-year period. Prevalence of stones containing AAU crystals and predominantly AAU stones were 3.1% and 0.2%, respectively. In more than two thirds of cases, AAU crystals represented less than 10% of stone crystal composition. No pure AAU stone was found. According to crystalline predominance, 42%, 35%, and 12% of these calculi were uric acid, infectious, and calcium oxalate stones, respectively. AAU crystals were detected as discrete intercrystalline or peripheral deposits in 74.4% of stones. In only one calculus was AAU crystals detected in the nucleus. The hospital charts of 37 patients who presented with 43 calculi containing AAU crystals were also reviewed. The mean age was 53.1 ± 16.6 years. Fifty-seven percent of calculi were upper urinary tract stones and 43% were bladder stones. Upper urinary tract calculi were more frequently uric acid stones, followed by infectious and calcium oxalate stones. Lower urinary tract calculi were more frequently infectious stones, followed by uric acid stones. Upper urinary tract stones were passed spontaneously in 13 patients and removed surgically in nine patients. Nine of these subjects were idiopathic recurrent stone formers who had passed other calculi with no trace of AAU crystal. Fifty-seven percent of lower urinary tract stones were associated with documented bladder dysfunction. In conclusion, although AAU-containing urolithiases are occasionally seen in our population, predominantly or primarily AAU stones are exceptional. AAU crystal formation usually appears as a minor and secondary phenomenon of no primary pathophysiologic relevance in stone formation.

Infrared spectrometric analysis of endemic bladder stones in Niger.

The composition of 42 bladder stones from young children in Niger has been determined by infrared spectrometry. Nucleus and subsequent layers were analyzed separately. The major constituents of the stones were ammonium acid urate (AAU) and calcium oxalate monohydrate (COM). The nucleus consisted of nearly pure AAU in 17 stones (40%) and it was found to be the major constituent of the nucleus in 8 other stones (19%). Furthermore, it was present as a minor constituent of the center in another 9 stones (21%). In only 3 calculi (7%) the nucleus consisted of pure COM. This study suggests that (a) AAU is the initiating material for nucleation in this stone type in Niger, and (b) the incidence of endemic bladder stone disease is higher in Africa than previously reported.

Thermal analysis of renal stones

The chemical composition of 200 renal stones, collected from Taxila, Rawalpindi and Islamabad regions in Pakistan, was determined by thermogravimetric (TG) and differential thermal analysis (DTA) techniques. The thermal curves show weight losses at various temperatures indicating dehydration and decomposition phenomena of renal stones. Results were compared with qualitative data obtained by IR analysis which confirmed the chemical composition of various stones in the solid state. The thermal curves helped in the differentiation of various kinds of water held by stones and their chemical composition was obtained by weight loss during pyrolysis. It was found that 26.5% of the stones were pure whewellite, 3% weddellite, 13% uric acid anhydrous, 7.5% struvite, 2.5% ammonium acid urate, 0.5% cystine and 47% stones had mixed composition. In the mixed state the most frequent combinations were those of calcium oxalate with uric acid (14.5%) and with phosphates (27.5%).

Urolithiasis in Northeast Bombay: Seasonal prevalence and chemical composition of stones

The seasonal prevalence of urinary calculus disease from the records of L.T. Municipal General Hospital, Sion, Bombay, which primarily caters services to poor people of Northeast Bombay, especially Dharavi slum area, is reported. The qualitative and quantitative compositions of stones collected from the patients of Dharavi slum area are also described. Interestingly, the prevalence of bladder stones (BSF) was lower than that of upper urinary tract stones (UUTSF) which suggests the possibility of involvement of environmental pollution. As regards total number of stone patients, a sharp fall in male BSF in March and increase in male UUTSF in November were evident. In females the number was maximum in April in both BSF and UUTSF. However, no recognizable pattern of seasonal variation was seen in operated stone patients indicating that metabolically active disease is unrelated to season. Prevalence of bladder stones in children was high and male/female ratio was about 5. All stones were of the mixed type. Infection was not a major contributor of stone growth. Calcium oxalate was the major constituent and ammonium acid urate was present in the majority of stones.

Childhood Urolithiasis in Iran with Special Reference to Staghorn Calculi

Between 1972 and 1984 148 children with urolithiasis were studied and managed at the University Clinic Children's Hospital of Teheran. In 125 children the calculi were in the upper and in 23 children in the lower urinary tract. The maximum incidence was between the ages of 5-8 and 12 years. 25 children had malformations and 16 had metabolic disorders. Cystinuria was observed in 6 and xanthinuria in 3 cases. The main constituents of calculi analyses in the upper urinary tract were calcium oxalate followed by ammonium acid urate. In the lower urinary tract ammonium acid urate and oxalate were seen with equal frequency, followed by uric acid. 16 children had staghorn calculi with an age profile of 5-13 years. Predominant symptoms were flank pain and gross hematuria. In 4 cases the calculi were bilateral. The calculi were removed successfully by pyelotomy and extensive pyelolithotomy. In 2 cases with more branched-out staghorn calculi and separate fragments, a logitudinal extensive nephrotomy was performed. In the absence of recurrent stones, renal growth and function were satisfactory postoperatively. In the majority of the cases the analyses of the staghorn calculi revealed phosphate.

Comparative in vitro encrustation studies of biomaterials in human urine.

A new dynamic in vitro human urine model was developed to compare biomaterial encrustation. The model incorporates a capacity to study seven biomaterials, a daily urine inflow of 500 ml, a reservoir capacity of 700 ml, and a turnover rate of four days. Encrustation studies performed for 2 weeks in sterile and infected (Proteus Vulgaris) urine on segmented polyether polyurethane, polyester polyurethane, silicone (Mitsui), silicone (Dow Corning), biothane, biolor 1 and biolor 11 demonstrated that biolor 11 (silicone-carbon composite) caused the least encrustation. Encrustation analysis showed brushite in the sterile model and struvite and ammonium acid urate in the infected mode I. Biolor II should have beneficial applications in catheters, stents and prosthetics which come in contact with urine.