Clinical significance of phosphate in calcium oxalate renal stones

We analysed calcium, magnesium, oxalate, citrate, urate and creatinine in urine and calculated risk factors in patients who had formed stones composed of calcium oxalate, and calcium phosphate, alone or as a mixture. Patients producing pure calcium oxalate stones (less than 0.1% phosphate) had a higher oxalate, and lower calcium excretion than stone-free subjects and patients forming other stone types. In contrast, patients producing calcium oxalate stones containing phosphate, even in trace amounts (greater than 0.1%) had no increase in oxalate excretion, but a higher calcium excretion than stone-free subjects. We could not correlate any computed variable (e.g. AP(CaOx) index) to stone composition. We conclude that pure CaOx stones may be the result of a high oxalate excretion, and that other calcium containing stones may have another and probably more complex aetiology, including primary precipitation of calcium phosphates.

Crystalluria determined by polarization microscopy. Technique and results in healthy control subjects and patients with idiopathic recurrent calcium urolithiasis classified in accordance with calciuria

A retrospective study was done on the nature and degree of crystalluria in spontaneously voided fasting and postprandial urine of patients with recurrent idiopathic calcium urolithiasis (RCU) divided into normocalciuria (20 males, 20 females) and hypercalciuria patients (20 males, 20 females), and controls (20 males, 20 females). The crystals were obtained using a filter technique and identified by microscopy. In addition, individual data, clinical chemistry variables and indices reflecting the risk of calcium phosphate and calcium oxalate crystallization were evaluated. In contrast to findings of other investigators of crystalluria we observed only a few crystals on the filters. The most frequently occurring phases were (in this order) a urate-containing phase (tentatively termed uric), an amorphous calcium phosphate phase (tentatively termed isotropic) and a phase of spheroid-like particles, not yet definitely characterized (tentatively termed spheroid). Calcium oxalate crystals were found only exceptionally. There was no relationship between the degree of calciuria (normo- versus hypercalciuric RCU) and crystalluria. Among RCU, males generally had a predominance of the isotropic, females of the spheroid phase, as compared with controls. Also, RCU females were generally obese, and their spheroid score and lean body mass correlated negatively and significantly. The calcium phosphate and calcium oxalate risk indices were always low in normal individuals, higher in RCU. Patients of both sexes with urinary stones had normal parathyroid gland function, but higher total calcium in fasting serum and higher urinary pH as compared with controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Seasonal variations in urinary risk factors among patients with nephrolithiasis

Twenty-four hour urine specimens from 5,677 stone-forming patients throughout the United States were analyzed for seasonal variations in urinary risk factors for nephrolithiasis. Determinations were performed for urine volume, pH, calcium, oxalate, phosphorus, sodium, magnesium, citrate, sulfate, uric acid, and the relative supersaturation (RS) of calcium oxalate, brushite, monosodium urate, and uric acid. Criteria for significant seasonal variation included a significant difference in monthly means of risk factors, seasonal grouping of the data by the Student-Newman-Keuls multiple range test, consistent year-to-year trends and a physiologically significant range. Minimum urine volume of 1.54 +/- 0.70 SD L/day occurred in October while a maximum urine volume of 1.76 +/- 0.78 SD L/day was observed during February. Minimum urine pH of 5.94 +/- 0.64 SD was observed during July and August while a maximum pH of 6.18 +/- 0.61 SD was observed during February. Daily urinary excretion of sodium was lowest during August, 158 +/- 74 SD mEq/day and highest during February 177 +/- 70 SD mEq/day. The RS of brushite and uric acid were found to display significant pH-dependent seasonal variation with a maximum RS of uric acid 2.26 +/- 1.98 SD in June and a low of 1.48 +/- 1.30 SD in February. Maximum RS of brushite 2.75 +/- 2.58 was observed during February. Minimum RS of brushite 1.93 +/- 1.70 SD was observed in June. Phosphorus excretion displayed seasonal variation about a spring-fall axis with a maximum value 1042 +/- 373 SD mg/day in April and a minimum value of 895 +/- 289 SD mg/day. Urine volume, sodium, and pH were significantly lower during the summer (June, July, August) than in the winter (December, January, February). The RS of uric acid was higher, but that of brushite and monosodium urate was lower in the summer than in the winter. The seasonal changes observed in urine volume, pH, sodium, and the RS of brushite and uric acid are consistent with summertime sweating and increased physical activity. Seasonal variations in phosphorus excretion are probably dietary in origin. The summertime was characterized by an increased propensity for the crystallization of uric acid but not of calcium oxalate or calcium phosphate.

How variations in the composition of urine influence urease-induced crystallization

To Study how the composition of urine influences urease-induced crystallization, human urine samples were incubated with urease and the subsequent precipitation measured. Beside the pH increase, the urinary content of magnesium and calcium had profound effects on the precipitation of magnesium ammonium phosphate and calcium phosphate, respectively. Urine phosphate, ammonium and osmolarity had no direct effects on the precipitation. Among the urine components with potential inhibitory properties, only albumin was found to be correlated with such an effect. This inhibitory activity was especially influential in urines with high calcium and magnesium levels. These findings suggest that the composition of urine could also influence the formation of stones consisting of magnesium ammonium phosphate and calcium phosphate.

Measurements of urinary state of saturation with respect to calcium oxalate and brushite (CaHPO4.2H2O) in renal stone formers

Urinary supersaturation with respect to calcium oxalate and/or brushite (CaHPO4.2H2O) is critical for the formation of calcium stones. The aim of this study is to use concentration product ratio (CPR) as a tool to assess the state of urine saturation with respect to calcium oxalate and brushite. One 24-h urine specimen from each of 16 healthy city dwellers (GI), 18 healthy villagers (GII) and 28 villagers with renal stones (GIII) was collected and analyzed for calcium, sodium, potassium, phosphate, uric acid, citrate and oxalate. The CPRs of calcium and oxalate and of calcium and phosphate before and after equilibration of the urine with the corresponding seeding crystals were also determined. Urinary volume and the excretion rate of calcium, potassium, uric acid, citrate and oxalate of GII and of sodium, phosphate, uric acid and citrate of GIII were significantly less than those of GI. The CPRs for calcium oxalate and brushite were 2.9 +/- 0.3 and 1.7 +/- 0.2 for GI, 2.7 +/- 0.2 and 1.3 +/- 0.1 for GII and 2.5 +/- 0.2 and 1.1 +/- 0.1 for GIII, respectively. The CPR values indicated that urine of all groups was generally supersaturated with respect to calcium oxalate salt (CPRs were above 1) and were not different among the groups. With regard to brushite, urine was also supersaturated but the state of supersaturation was less than that of calcium oxalate. Furthermore, instead of being supersaturated, brushite in many urine specimens of GIII was undersaturated and its mean CPR was even significantly less than that of GI (P less than 0.01).

Chemical measurement of calcium oxalate crystalluria: results in various causes of calcium urolithiasis

Calcium oxalate and calcium phosphate crystalluria have been measured chemically in 1,173 urine samples whose chemical compositions were also analysed. The importance of urinary oxalate as a determinant for calcium oxalate crystalluria was confirmed. Significant concentrations of calcium oxalate crystals may be present in urine even though the crystals are too small for detection by light microscopy or by many particle-counting methods. Calcium phosphate crystals in urine always contain a small proportion of calcium oxalate. Results in various clinical situations are reviewed.

Urinary supersaturation with respect to brushite in patients suffering calcium oxalate lithiasis

The urines of 23 stone-formers presenting repeated calcium oxalate lithiasis and 12 control subjects were collected at six different time periods daily. Supersaturations for calcium oxalate and brushite (DCPD) were calculated using ionic and solubility products. Urines of both groups were supersaturated for calcium oxalate but only urines of the stone-formers were supersaturated for brushite, the most simple calcium phosphate which nucleates very easily at the urinary pH. This fact suggests that the core of the calcium oxalate stone could be made of either a calcium oxalate crystallite or a brushite seed onto which hetergeneous nucleation of calcium oxalate can take place.

Measurement of calcium phosphate crystalluria: influence of pH and osmolality and invariable presence of oxalate

Calcium phosphate and calcium oxalate urinary crystal concentrations in normal and stone-forming subjects were measured. The urinary crystals were examined by light microscopy and urine samples were analysed for oxalate, pH and osmolality. Calcium phosphate crystal concentrations were clearly related to urine pH but unrelated to urine osmolality. An unexpected finding was co-precipitation of oxalate with calcium phosphate. Consequently, precipitated invariable oxalate increased with rising urinary pH. Possible explanations and implications are discussed.

The effects of citrate on hydroxyapatite induced calcium oxalate crystallization and on the formation of calcium phosphate crystals

The addition of different amounts of hydroxyapatite crystals (HAP) to a solution, metastably supersaturated with respect to calcium oxalate (CaOx) resulted in heterogenous crystallization at seed concentrations exceeding 0.2 mmol/l. The induction period varied between 1 and more than 8 h with the shortest period for a seed concentration of 2 mmol/l. Addition to the system of 1 and 2% of whole urine and citrate in concentrations corresponding to approximately 1% of that found in normal urine inhibited the crystallization for as long as 4 h. In a system supersaturated with respect to calcium phosphate (CaP) the total number of crystals was markedly reduced by citrate concentrations exceeding 0.5 mmol/l. The fractions of medium sized and large crystals were sharply reduced and small crystals predominated at higher citrate concentrations. This might indicate effects of citrate on both crystal growth and crystal aggregation. We conclude that increased citrate concentrations during treatment with alkali leads to a significant inhibition of CaOx growth on HAP as well as to a prevention of the formation of large CaP crystals from solutions supersaturated with respect to CaP.

[Clinical significance of phosphaturia]

From September 1986 to August 1987, heavy precipitation of amorphous calcium phosphate, that is phosphaturia, was found at our outpatient clinic in 153 postprandial urine specimens from 115 patients, in 1.5% of all the specimens examined during this period. One patient was excluded because he had both urolithiasis and urinary tract infection. The remaining 152 specimens with phosphaturia were then divided into 3 groups; Group I from patients with urolithiasis, Group II from patients with urinary tract infection and Group III from patients without either urolithiasis or urinary tract infection (Phosphaturia Group, Table 1). It is evident from this table that phosphaturia is repeated more frequently in patients with urolithiasis than in patients without urolithiasis (p less than 0.01). 200 urine specimens examined during this period were selected randomly. Three bloody or purulent specimens were excluded. The remaining 197 specimens from 189 patients were divided into 3 groups, as in the phosphaturia group (Control Group, Table 2). When the proportion of the number of specimens to the total is compared between the phosphaturia group and the control group, it is clear that phosphaturia is found more frequently in specimens from patients with urolithiasis than in specimens from patients without urolithiasis (p less than 0.01). Since phosphaturia was almost always found in the specimens with urine pH greater than or equal to 7, 486 patients, in whom the pH of the first urine specimen was equal to or above 7, were selected from among 1434 patients undergoing urinalyses during this period and divided into 3 groups as has been described above (Table 3).(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of glucose intake on urine saturation with calcium oxalate, calcium phosphate, uric acid and sodium urate

The effect of simple carbohydrate intake on the state of urine saturation was studied in 44 patients with calcium kidney stones and in 28 healthy subjects. Renal excretion of calcium, magnesium and oxalate significantly increased and pH of urine decreased after an intake of 100 g glucose in stone formers and healthy subjects. In the basic conditions (before glucose administration) urine was supersaturated with calcium oxalate in stone formers (median 0.55) and healthy subjects (0.24; p less than 0.05). Carbohydrate intake caused a significant increase of the degree of urine saturation with calcium oxalate and uric acid. The degree of urine saturation with brushite and sodium urate after glucose administration did not change. These data suggest that excess of simple carbohydrate consumption may increase the degree of urine saturation with some of the compounds important in stone formation.

Procedure for the measurement of calcium oxalate and phosphate crystals in urine

A method is described for the chemical measurement of calcium oxalate and phosphate crystal formation in urine. The crystals were centrifuged, washed and the oxalate measured by an immobilised oxalate oxidase technique and the phosphate by a standard centrifugal analyser procedure. The methods proved precise and recoveries were good. Calcium oxalate crystal formation after evaporation is time-dependent and this parameter must therefore be standardised. Values for normal urinary calcium oxalate crystal concentration after concentration are given.

Alkali action on the urinary crystallization of calcium salts: contrasting responses to sodium citrate and potassium citrate

Alkali therapy is used commonly to prevent recurrent stone formation in patients with distal renal tubular acidosis. We compared the effects of potassium citrate to those of sodium citrate in 6 well defined cases of incomplete distal renal tubular acidosis. The patients were studied during a control phase, during potassium citrate treatment (80 mEq. per day) and during sodium citrate treatment (80 mEq. per day) chosen in random order. Potassium citrate caused a decrease in urinary calcium and a significant increase in urinary citrate that resulted in a significant decrease in the urinary saturation of calcium oxalate. It did not alter the saturation of brushite and sodium urate. However, while sodium citrate also was able to increase the urinary citrate level, there was no decrease in the urinary calcium (owing to the increased sodium load). Thus, the urinary saturation of calcium oxalate did not decrease as much as with potassium citrate and the saturation of brushite increased significantly. Moreover, the urinary saturation of sodium urate increased significantly owing to the enhanced sodium excretion. The results suggest that potassium citrate therapy may retard the crystallization of calcium oxalate and may not cause calcium phosphate crystallization. In contrast, sodium citrate may have no effect or it sometimes may accentuate the crystallization of calcium salts. Thus, our study supports the potential clinical advantage of potassium citrate therapy over sodium alkali treatment in patients with incomplete distal renal tubular acidosis and recurrent calcium nephrolithiasis.

Effect of prolonged bedrest on the propensity for renal stone formation

The effect of prolonged bedrest immobilization on urinary risk factors for stone formation and on the propensity for the crystallization of calcium salts was examined in eight normal subjects. During 5 weeks of bedrest, the mean urinary calcium excretion rose during the first week and remained elevated (from 5.68 to approximately 7.50 mmol/day). Mean urinary phosphorus excretion increased by the second week of bedrest and remained elevated (from 2.70 to approximately 30.6 mmol/day). Urinary sodium and uric acid excretion rose slightly, as did urinary magnesium. Urinary pH, oxalate, and citrate changed slightly or not at all. Owing to these biochemical alterations, urinary saturation of calcium phosphate, calcium oxalate, and monosodium urate increased significantly during bedrest, but that of uric acid did not change. The inhibitor activity against the spontaneous nucleation of brushite (CaHPO4.2H2O) and calcium oxalate was not altered significantly by bedrest. Thus, the propensity for the crystallization of stone-forming calcium salts was enhanced by bedrest, suggesting that immobilization may confer increased risk for the formation of calcium-containing renal stones.

Influence of calcium content in mineral water on chemistry and crystallization conditions in urine of calcium stone formers

19 idiopathic recurrent calcium stone formers were examined on a constant diet supplemented with mineral water of high (386 mg/l) and low (10 mg/l) calcium content. The effects of calcium and oxalate loading were studied separately. Ingestion of mineral water with high calcium content lead to an increase of urinary calcium and a decrease of urinary oxalate compared to mineral water with low calcium content. On the calcium-rich mineral water, urinary saturation with Whewellite was lower and it hardly reached the critical level for calcium oxalate crystallization after oxalate loading, which was in contrast to the results on low calcium mineral water. Urinary Brushite saturation was generally low and showed no significant differences between the two mineral waters.

Study of calcium phosphate crystalluria

When the frequency of heavy calcium phosphate crystalluria was compared among postprandial urine specimens collected from 152 healthy persons (group 1) and 108 patients with calcium urolithiasis (group 2), there was no significant difference between these groups. However, the frequency of crystalluria was significantly greater in 49 patients in group 2 who required or had required surgical intervention for calcium stone disease than in group 1 (p less than 0.05). Calcium phosphate precipitates collected from 7 urine specimens by repeated centrifugation were studied by infrared, X-ray, thermal and electron probe analyses. The principal component of the precipitates was poorly crystallized apatite associated with some organic material. The precipitates from the 7 samples appeared as aggregates of fine spherules less than 1 micron. in diameter, and the calcium-to-phosphate molar ratio of a spherule ranged from 1.02 to 1.19. We conclude that not only calcium oxalate crystalluria but calcium phosphate crystalluria may have an important role in the formation of urinary stones.

Fasting gastrinemia and elevated supersaturation with hydroxyapatite of fasting urine--observations in renal calcium stone patients and controls

We evaluated serum gastrin, acid-base status, variables of mineral metabolism in fasting blood, as well as pH, relative supersaturation of stone forming constituents, and crystalluria in the associated fasting urine, of control subjects (n = 12), and in age- and weight-matched male normocalciuric (n = 12) and hypercalciuric (n = 12) patients with idiopathic recurrent calcium urolithiasis (RCU). In RCU, mineral metabolism and acid-base data are unchanged, whereas mean serum gastrin is only insignificantly higher as compared to controls. Subclassification of all participants into categories with either high-normal or low-normal gastrin reveals that in RCU with low-normal gastrin there is a higher-than-normal urinary pH and significantly elevated supersaturation of urine with hydroxyapatite. Crystalluria and stone analysis support the assumption that the physico-chemical environment accompanied by low gastrin levels predisposes to urinary precipitation of calcium phosphate with subsequent formation of a stone nidus. pH in fasting urine and integrated fasting serum gastrin correlate significantly, suggesting that low fasting serum gastrin in RCU patients may be considered a risk factor for calcium phosphate stone formation.

Measurement of the risk of calcium phosphate crystallization in urine

A method is described for analysis of the risk of calcium phosphate (CaP) crystallization in urine samples. The pH required for formation of 500 crystals in the size range 3.5 to 5 micron (pHCaP) was determined in a Coulter Counter following addition of sodium hydroxide. The risk of CaP crystallization (CaP-CR) was defined as: 1/(pHCaP--5.8). CaP-CR was determined in 24 h urine collections from 25 patients with calcium stone disease and 26 normal subjects, each urine diluted to a creatinine concentration of 5 mumol per ml. The mean (+/- SD) CaP-CR was 0.71 +/- 0.18 and 0.63 +/- 0.14 respectively and did not differ significantly. This method might be useful for evaluations and follow-up of stone formers with respect to the risk of CaP precipitation and stone formation.

Chemical factors governing the state of saturation towards brushite and whewellite in urine of calcium stone formers

Variations of urinary pH and concentrations of calcium, phosphate, oxalate, magnesium and citrate have been produced by 4 different diets given to 19 idiopathic calcium stone formers. The state of saturation towards whewellite and brushite was directly measured in the 76 urine samples by equilibration with the corresponding salts and was compared to chemical constituents by regression analyses. The state of saturation towards calcium oxalate monohydrate was significantly governed only by the urinary oxalate concentration, and a soluble oxalate fraction not contributing to calcium oxalate chelation was demonstrated. The state of saturation towards brushite was exclusively determined by urinary calcium and pH, the latter below 5.5 showing a high influence on brushite solubility.

Urine composition and stone formation during treatment with acetazolamide

Twelve patients who formed renal stones during acetazolamide treatment for glaucoma were studied. Calcium phosphate was the dominating component in the stones. Long term treatment with acetazolamide decreased urinary citrate markedly, which will result in an increased ion-activity product of calcium phosphate and a decreased inhibiting property of urine on calcium phosphate crystallization. The treatment also increased urinary oxalate which together with a low citrate might increase the risk of calcium oxalate crystallization. However, an estimate of the ion-activity product of calcium oxalate in urine (AP [CaOx]-index) was unaffected by the treatment and calcium oxalate was a minor component of the stones.

Crystalluria in marathon runners. 1. Standard marathon--males

Epidemiological evidence suggests that marathon runners have a higher incidence of renal stone formation than occurs in the general population. Since crystalluria and stone disease are thought to be related, we subjected urine samples from a group of marathon runners to particle counting and sizing in a Coulter Counter equipped with a population accessory unit. The volume-size distribution curves so obtained were bimodal with one peak occurring in the 2-5 micron diameter range and a second in the 15-32 micron diameter range - a pattern that is remarkably similar to the distributions reported for recurrent idiopathic stone formers and distinctly different to those recorded for control subjects. Analyses by scanning electron microscopy and X-ray powder diffraction revealed other features which are regarded as typical of stone formers' crystalluria. These physicochemical data indicate that marathon runners may be at increased risk of urinary stone formation.