Urinary supersaturation of calcium oxalate and phosphate in patients with X-linked hypophosphatemic rickets and in healthy schoolchildren.

UNLABELLED: Nephrocalcinosis (NC) is a complication of the treatment of X-linked hypophosphatemic rickets (XLHR). Some studies have found that treated patients have enteric hyperoxaluria caused by phosphate therapy and have implicated calcium oxalate, whereas others have found only calcium phosphate in renal biopsy tissue. AIM AND METHODS: We aimed to study the urinary supersaturation of calcium oxalate and calcium phosphate and to determine whether these measures are risk factors for NC. We collected 24-hour urine samples from 20 patients (12 girls) with XLHR, mean +/- SD age 8.2 +/- 4.7 years, and from 79 age-matched members of a healthy control group prospectively. RESULTS: The median 24-hour urine excretions of oxalate, phosphate, and citrate (mmol/1.73 m(2) per day) were significantly increased in patients compared with the control group (oxalate 0.38 vs 0.28, P =. 0012; phosphate 63.1 vs 25.8, P <.0001; citrate 4.18 vs 2.7, P =. 0002). However, no significant differences were seen in the calcium oxalate or calcium phosphate between patients and the control group. No significant differences were seen in 24-hour urine calcium or magnesium excretion between patients and the control group; however, 8 patients had hypercalciuria. A significant higher urine volume in patients compared with the normal group (826 mL/m(2) 24-hour vs 597 mL/m(2) 24-hour; P <.005) was found. Twelve patients had NC at the time of investigation, and although the oxalate excretion was significantly higher in these patients, no significant difference was seen in the relative supersaturation of calcium oxalate monohydrate (CaC(2)O(4).H(2)O) compared with the 8 without NC. CONCLUSIONS: Although 24-hour urine oxalate and phosphate excretion are increased in treated patients with XLHR, there is no increase in the supersaturation of either calcium oxalate or phosphate. Determination of the supersaturation of calcium oxalate or calcium phosphate does not predict the development of NC in XLHR.

The physicochemical basis of urinary catheter encrustation.

OBJECTIVES: To determine the relationship between urinary pH and Ca2+ solubility in urine samples from patients who experienced either frequent ('blockers') or infrequent ('nonblockers') catheter blockage by crystalline deposits of divalent cation salts. MATERIALS AND METHODS: Fresh urine samples from 'blockers' and 'nonblockers' were collected and the ionic calcium concentration ([Ca2+ ]) measured using a Ca2+-selective electrode whilst the urinary pH was increased in 0.25 increments between 4.75 and 9.00. The pH at which crystallization occurred (nucleation) was determined and crystal composition analysed. RESULTS: The mean (sd) voided urinary pH of catheter 'blockers' was significantly more alkaline than that from 'nonblockers', at 7.63 (0.64) and 5.97 (0.80), respectively (P=0. 001). The nucleation pH of catheter 'blockers' was significantly more acid than in 'nonblockers', at 7.43 (0.73) and 6.45 (0.65), respectively (P=0.005). Urine from 'blockers' had significantly more Ca phosphate and Mg ammonium phosphate crystals. 'Blockers' were further divided into two subsets with and without urease-based urinary tract infection; both showed a decrease in the nucleation pH. CONCLUSION: In the urine from 'nonblockers' there is a wide safety margin between voided and nucleation pHs; this margin was less in the urine from 'blockers'. This reduction in the safety margin arises partly because the voided pH in those with a urinary tract infection is more alkaline. However, the decrease in the nucleation pH also suggests that a fundamental property of urine is altered, which reduces Ca2+ solubility at more neutral pH values. The long-term goal is to increase the nucleation pH of catheter 'blockers' and increase the margin of safety.

Effects of Tamm-Horsfall protein with normal and reduced sialic acid content upon the crystallization of calcium phosphate and calcium oxalate in human urine.

OBJECTIVE: To examine the effects of Tamm-Horsfall protein (THP) of normal and low sialic acid content on urinary crystallization, and establish whether there are changes conducive to the formation of kidney stones. MATERIALS AND METHODS: Purified samples of THP were recovered from the urine of non-stone forming individuals. A portion of each THP sample was treated with the enzyme neuraminidase to yield the low sialic acid form of the protein. The two forms of THP were added separately to ultrafiltered urine and crystallization was then induced in the urine by evaporation at 37 degrees C. Two types of experiment were then conducted with the crystals that formed; the rate at which the resulting calcium phosphate or calcium oxalate crystals sedimented in the evaporated urine was determined and the proportion of these crystals and protein which was retained when the urine was passed through a 75 microns sieve was measured. RESULTS: Calcium phosphate and calcium oxalate crystals remained in stable colloidal suspension in ultrafiltered urine when in the presence of normal THP; these suspensions passed freely through the 75 microns sieves. When crystals formed in the presence of low sialic acid THP, the sedimentation was rapid and the crystals were readily retained with protein on the sieves. CONCLUSIONS: These results indicate that whilst normal THP inhibits urinary crystal aggregation, the properties of the low sialic acid form are consistent with the promotion of crystal aggregation and hence stone formation.

The inhibitory activity of some citrate analogues upon calcium crystalluria: observations using an improved urine evaporation technique.

The ability of three compounds, all similar in chemical structure to citric acid, to decrease calcium crystalluria has been measured. The measurements were made in normal human urine at 37 degrees C and compared with the crystal-decreasing power of citric acid when measured in the same way and in the same urine samples. One of the compounds tested, phosphocitric acid, was more potent than citric acid in inhibiting calcium oxalate crystal precipitation. At higher concentrations it also proved more effective against calcium phosphate. A urine evaporation method was used to carry out the crystal inhibition tests after modification to improve its precision.

Rapid computer-assisted infrared analysis of urinary calculi using photoacoustic detection.

The application of commercial spectrum-analysing software to quantitative analysis of urinary stones by Fourier transform infrared spectrophotometry is described. The infrared technique is straightforward in comparison with other stone analysis procedures of similar scope and affords significant time savings. The use of partial least squares regression in the analysis program enables better quantitation of stone components than has been hitherto possible using infrared methods. All the principal and many less common stone constituents can be detected and measured. Photoacoustic detection was employed, thus enabling non-destructive analysis with minimal sample preparation. A comparison is made between the infrared procedure and the hybrid thermogravimetric plus "wet" chemistry technique, which it has superseded for routine urinary stone analysis in the author's department.

Risk factors for calculus formation in patients with renal transplants.

OBJECTIVE: To investigate the risk factors for stone formation in patients with functioning renal transplants in whom renal calculi develop. PATIENTS AND METHODS: Renal calculi developed in six of 178 patients with functioning renal transplants under current review, an incidence of 3%. Risk factors for stone formation were investigated in five of these patients and compared with a randomly selected control group of 41 transplant patients with no stone problems. RESULTS: Patients with transplant calculi typically passed smaller volumes of significantly more concentrated and alkaline urine with greater urinary excretion of uric acid (P < 0.05). Urine calcium excretion was also increased. Crystalluria was present in three of five stone formers compared with two of 25 controls. Overall, metabolic abnormalities included hypocitraturia (75%), hyperparathyroidism (36%), hypophosphataemia (24%) and hypercalcaemia (10%). Urinary infection was common (50%) and urinary output of magnesium and phosphate was at the lower end of normal for all patients. CONCLUSION: These results suggest a multifactorial aetiology for stone formation in renal transplant recipients. Approaches to prevention and management are discussed.

Chemical analysis of post-lithotripsy stone fragments: a critical evaluation.

A scheme for the chemical microanalysis of renal stone fragments recovered from urine voided immediately after lithotripsy has been developed and evaluated. The analytical procedure includes assay of calcium, magnesium, phosphate, oxalate and urate and has been applied to 78 such urine samples. Problems relating to co-existing crystalluria and blood and urine contaminants have been recognised and overcome. However, significant loss of all stone components due to fragment dissolution in urine prior to recovery was found to occur and was investigated. The distribution of stone components found in these analyses was similar to that seen in previous surveys of intact stones.

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.

Risk factors for urinary calcium oxalate crystals as revealed by their specific enzymatic assay.

Calcium oxalate crystal concentrations were assayed by a new highly specific enzymatic method in 1200 urine samples from normal subjects and stone formers. Examination of the crystals was also carried out by light microscopy and urines were analysed for oxalate, calcium, magnesium, citrate, urate, pH and osmolality. A striking positive correlation was established between urinary oxalate concentration and calcium oxalate crystal concentration as well as incidence of calcium oxalate crystals and aggregates seen by microscopy. A less striking relationship, also supported by light microscopy, was found between calcium oxalate crystal concentration and urinary calcium concentration. A small rise in calcium oxalate crystalluria was seen with increasing osmolality, but no relationship found between concentration or urinary urate, citrate or magnesium and that of calcium oxalate crystals. Higher levels of calcium oxalate crystal concentration appeared in alkaline urines in association with calcium phosphates. The dominance of urinary oxalate as a risk factor for calcium oxalate crystalluria is confirmed.

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.

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.

Reduction of the urinary risk factors of urolithiasis with magnesium and tartrate mixture: a new treatment.

Magnesium and tartrate each reduce calcium oxalate crystal formation in urine. Since the effects are additive, a palatable mixture of magnesium and tartrate salts was devised and fed to 6 healthy volunteers. There were no side effects. There was a moderate fall in urinary calcium, moderate rises in urinary magnesium, tartrate and citrate, and no change in urinary oxalate. Hence there are good grounds for supposing that this mixture could be used to prevent urinary stone recurrence.

Pyrophosphate does not influence calcium oxalate or calcium phosphate crystal formation in concentrated whole human urine.

1) Low pyrophosphate urine was generated by passage through a nylon coil bearing immobilised inorganic pyrophosphatase. High pyrophosphate urine was made by addition of inorganic pyrophosphate. 2) Urine samples of low, normal, and high pyrophosphate content were rapidly evaporated at 37 degrees C to 1,050 or 1,250 mosmol/L and the crystals formed studied by microscope, isotope and chemical methods. 3) Urinary pyrophosphate level had no significant effect upon calcium oxalate crystals formed in whole urine at pH 5.3 or 6.1, or calcium phosphate crystals formed at pH 6.8.

Raising urinary citrate lowers calcium oxalate and calcium phosphate crystal formation in whole urine.

Crystal formation in whole urine was studied by the technique of rapid evaporation to 1,250 mosmol/l with and without raising citrate concentration by 40-50%. The added citrate reduced calcium oxalate crystal formation at pH 5.3 by about 25% and reduced calcium phosphate crystal formation at pH 6.8 by some 42%. These results support the view that citrate is important in maintaining calcium in solution in whole urine, and that raising the urinary citrate could be effective treatment for calcium oxalate/phosphate urolithiasis.

Urate does not influence the formation of calcium oxalate crystals in whole human urine at pH 5.3.

1. Samples of fresh human urine were treated with immobilized uricase to lower urate concentration. Urate was added to yield low, normal and high urate samples. 2. Each sample was rapidly evaporated at pH 5.3 to standard osmolality and the yield of calcium oxalate crystals measured either by semi-quantitative microscopy or fully quantitative radioisotope techniques. 3. Increase of urinary urate did not increase the calcium oxalate crystals formed and may even have had an opposite effect. 4. Allantoin was without significant effect upon calcium oxalate crystal formation. 5. These data provide no support for the suggestion that reducing urate concentrations in the urine may be of value in treatment of patients with calcium oxalate stones.

Magnesium reduces calcium oxalate crystal formation in human whole urine.

1. A low urinary magnesium was induced in normal volunteer subjects by giving cellulose phosphate; magnesium was added in vitro to yield urine samples of normal and high magnesium concentrations. 2. After rapid evaporation of these urine samples at pH 5.3 to standard osmolality the calcium oxalate crystals were measured by microscopy and isotopic methods. 3. There was a clear inverse correlation between magnesium concentration and calcium oxalate crystal formation. 4. The case for treating calcium oxalate urolithiasis with magnesium is strengthened.

Uromucoids and urinary stone formation.

Crystal formation was studied in fresh urine samples after rapid concentration to standard osmolarity in a rotary evaporator at 37 degrees C. Uromucoids promoted calcium oxalate and calcium phosphate crystal formation and also induced clustering of calcium phosphate precipitates. It is postulated that uromucoid precipitation is the first stage in stone formation. Minerals then deposit on the uromucoid precipitate and the whole complex becomes attached to the renal tubules.

A new urinary test for stone "activity".

Rapid evaporation of urine to osmolarity 1200 results in a high incidence of envelope Wedellite and calcium phosphate crystals. The Wedellite crystals closely resemble those seen in untreated urine samples of stone formers. The incidence of crystalluria produced by these tests is higher in the stone formers than in the normal subjects, reduced by thiazides and increased by cellulose phosphate; combined thiazide and cellulose phosphate therapy was most effective in reducing crystalluria. Simple calcium and oxalate concentration products were calculated and did not correlate well with incidence of calcium oxalate crystalluria. Although the product is important, inhibitors of crystal formation must be equally important. It is postulated, but not proven, that the evaporation tests may indicate normal subjects at risk to stone formation when exposed to chronic dehydration and whether a stone former is still metabolically active.

Seasonal variations in urinary crystals.

Individual urine samples from normal subjects and stone-formers with idiopathic hypercalciuria have been examined for crystals both qualitatively and quantitatively at 37 degrees C. The group as a whole showed a rise in incidence of urinary crystals in the summer months of June to August inclusive. This rise was seen most clearly in overnight urines, collected on rising in the morning, and the patients appeared to be at risk overnight during the summer. In the untreated patients the summer rise in incidence of phosphate crystals was quite dramatic but was only small in the cellulose phosphate treated group, who showed a rather constant and raised incidence of oxalate crystals right through the year. Seasonal crystal incidence has been compared with seasonal changes in urinary composition. The rise in crystal incidence during the summer was associated with increased creatinine concentration in the same urine samples and with increased oxalate concentration in 24-hour urine collections.

Seasonal variations in urinary excretion of calcium and oxalate in normal subjects in patients with idiopathic hyperclaciuria.

A longitudinal 9-year retrospective study of 24-hour urinary calcium values has been made in a metabolic stone clinic amongst patients with idiopathic hypercalciuria. No seasonal variations could be observed in contrast ot a previous study from Leeds, A prospective longitudinal study was made of 24-hour urinary calcium values in a small group of normal subjects. No seasonal variation could be ovserved. In the prospective study no seasonal variations in urinary oxalate could be observed. In a 2-year longitudinal study of stone patients with idiopathic hypercalciuria, urinary oxalate was found to be higher in the summer than in the winter. This was attributed to the combination of a higher intake of oxalate-rich foods in the summer, and the low calcium diet with which they were treated.