Hypercalciuria and hyperuricosuria in patients with calcium nephrolithiasis

Juvenile renal stone disease: a study of urinary promoting and inhibiting factors

Urinary excretion of the most widely studied renal stone promoting (calcium, oxalate, uric acid and phosphate) and inhibiting (citrate, magnesium, pyrophosphate and glycosaminoglycans) factors, as well as the Tamm-Horsfall mucoprotein, was evaluated in 14 children with idiopathic calcium nephrolithiasis, 6 children with renal stone disease secondary to excretory malformations and 19 normal controls. No statistically significant differences in urinary excretion of promoting and inhibiting factors were found in children with idiopathic calcium nephrolithiasis but the relationship between promoting and inhibiting factors was changed as shown by an abnormal ratio of oxalate/citrate X glycosaminoglycans. This finding suggests that there is an imbalance between promoting and inhibiting factors in children with idiopathic calcium nephrolithiasis, and it is not detected by assay of each single substance.

The stone clinic effect in patients with idiopathic calcium urolithiasis

The "stone clinic effect" refers to the effect of encouraging a high intake of fluid and avoiding dietary excesses on stone formation and growth in patients with urolithiasis. To determine the extent of this effect we reviewed the clinical courses of 108 patients with idiopathic calcium urolithiasis and indeterminant metabolic activity. There was no evidence of stone growth or new stone formation (metabolic inactivity) after a mean followup of 62.6 months in 63 of the 108 patients (58.3 per cent), including 12 of 17 (70.6 per cent) with hypercalciuria and 7 of 15 (46.7 per cent) with hyperuricosuria. Comparison of initial and followup 24-hour urine volumes demonstrated a significant increase in patients who were metabolically inactive at followup (p less than 0.0005), while no increase was detected in patients who were metabolically active at followup. We recommend that specific drug therapy should not be given to patients with idiopathic calcium urolithiasis until the stone clinic effect has been evaluated.

The influence of renal prostaglandins on urinary calcium excretion in idiopathic urolithiasis

Hypercalciuria is well recognized as an important factor in the cause of idiopathic calcium stone disease. Identification of the exact mechanism for the renal tubular handling of calcium has proved elusive, hence, treatment methods to alter the concentration of urine calcium in hypercalciuric stone formers have hitherto been non-specific. It is now well established that renal prostaglandins influence intrarenal hemodynamics and tubular electrolyte excretion. As the renal handling of sodium and calcium is intimately related, the possibility that the mechanism underlying hypercalciuria may be prostaglandin mediated was considered. Experiments were performed in conscious Sprague-Dawley rats (n = 10) to determine the changes in calcium excretion following prostaglandin synthetase inhibition with indomethacin. Calcium excretion was significantly reduced (p less than 0.01), compared with control animals (n = 10). Further experiments were performed in anesthetized monkeys (Macaca fascicularis) to see if the inhibitory effect of indomethacin was reversible. Exogenous prostaglandin (PGE2) infusion resulted in a marked calciuretic response without producing changes in glomerular filtration rate or blood pressure. Forty-three hypercalciuric patients were treated with a prostaglandin inhibitor for periods ranging from 2 to 4 weeks, and all showed a significant fall in urinary calcium excretion to within the normal range. This clinical and experimental study suggests that prostaglandin (PGE2) is a hormone which determines the renal handling of calcium by influencing renal tubular function.

Urinary excretion of urate in patients with calcium oxalate stone disease

The diurnal variation in excretion and concentration of urinary urate was studied in 31 patients with calcium oxalate stone disease. Urate excretion was highest during the day-time, decreased in the evening and was low during the night. Meal-related peaks were observed. The concentration of urate reached the highest levels during the morning hours and, attributable to a low pH in morning urine, most samples were at this time super-saturated with respect to uric acid. In addition, many urines appeared to be at high risk of exceeding the uric acid formation product. Concerning the ion-activity product of sodium urate, supersaturated samples were frequently found, but the risk of exceeding the formation product for sodium urate at a normal urate excretion was apparently low.

Pathogenesis and clinical course of mixed calcium oxalate and uric acid nephrolithiasis

By direct measurement, urine from patients who form calcium oxalate stones was supersaturated abnormally with respect to calcium oxalate monohydrate but not supersaturated with respect to undissociated uric acid. Urine from patients who form uric acid stones was supersaturated excessively with undissociated uric acid but not calcium oxalate. Patients who form both calcium oxalate and uric acid stones, however, produce urine that is supersaturated with respect to both solid phases. Low urine pH was the primary factor that increased supersaturation with respect to undissociated uric acid. The formation of both calcium oxalate and uric acid stones appears to be explained by a dual abnormality of urine supersaturation.

Effects of bendroflumethiazide on urate metabolism during treatment of patients with renal stones

Treatment with bendroflumethiazide (2.5 mg, twice daily with potassium supplements) in 63 patients with calcium-containing renal stones for a minimum period of 1 year (average duration of treatment 2.6 years) increased the serum urate values in all patients with an average of 90 mumol./l. (conversion factor: 1 mmol. urate = 183 mg.). Despite this the mean urinary urate excretion was unchanged. In the individual patient a systematic effect of therapy was evident since in patients with low pretreatment values the thiazide increased the urate output while in those with the highest levels before therapy it caused a reduction. In most patients there was a reduction of the urate clearance during therapy, which was most evident in those with the highest pretreatment clearance values. In patients with incomplete types of renal acidification defects the same effects were seen on urate metabolism during thiazide treatment as in the other, idiopathic, stone formers. Although the possible role of urate in calcium stone formation has not been definitely settled this study shows that thiazides do not cause hyperuricosuria and hence their beneficial effects on calcium excretion are not counteracted.

Should patients with single renal stone occurrence undergo diagnostic evaluation?

Diagnostic evaluation was conducted on 34 patients with a single episode of renal stone formation. Absorptive hypercalciuria as disclosed in 55.9 per cent (23.5 percent type I and 32.4 per cent type II), renal hypercalciuria in 11.8 per cent, primary hyperparathyroidism in 2.9 per cent, hyperuricosuric calcium oxalate nephrolithiasis in 8.8 per cent and no metabolic abnormality in 20.6 per cent. Compared to the group with recurrent stone formation the group with a single stone episode had just as severe biochemical abnormalities or laboratory results, such as hypercalciuria and exaggerated calciuric response to oral calcium load in absorptive hypercalciuria, high fasting urinary calcium and cyclic adenosine monophosphate in renal hypercalciuria, hyperuricosuria in hyperuricosuria calcium oxalate nephrolithiasis and low urine volume in no metabolic abnormality. The results suggest that the same physiological and environmental disturbances characterize stone formation in patients with a single stone episode as in those with recurrent stone formation and indicate the need for diagnostic evaluation.

Urinary excretion of urate in renal calcium stone disease and in renal tubular acidification disturbances

The 24-hour urinary excretion of urate was investigated in 467 consecutive stone formers - 350 males and 117 females - and 89 apparently healthy controls with no history of stone disease. Males had a higher urinary excretion of urate than females but there was no difference between stone formers and controls. Urinary urate decreased with advancing age. Patients with a proximal tubular acidification defect had a lower urate clearance than patients with a normal acidification of the urine. Patients with hyperuricosuria presented a higher frequency of stone operations but a lower stone episode rate than matched normouricosuric stone formers. Hyperuricosuria in combination with renal acidification defects was associated with the highest frequency of stone operations. Hyperuricosuric patients also had a higher excretion of calcium than normouricosuric patients. Hyperuricosuria is not a common feature of calcium stone disease but when present is associated with a more severe stone disease in terms of stone operations.

Factors that predict relapse of calcium nephrolithiasis during treatment: a prospective study

We evaluated 522 patients with idiopathic, recurrent calcium nephrolithiasis using a comprehensive clinical and laboratory protocol, and obtained additional laboratory measurements during their subsequent years of treatment in our program. In 57 patients, a new calcium stone ultimately formed during treatment (relapse), whereas 189 others have been free of recurrence during at least two years (average 4.3 +/- 2.2 [SD] years) of follow-up. Compared with the patients who remained stone-free, the patients with relapse (1) had a shorter interval between the time they entered our program and the time their last recurrent, pretreatment stone formed; (2) excreted more calcium *in mg/kg of body weight pr 24 hours) in their urine during treatment (2.79 +/- 1.08 versus 2.39 +/- 0.98 [SD] for relapse and stone-free); and (3) increased their urine volume less during treatment compared with pretreatment values (delta in liters per 24 hours was -0.02 +/- 0.48 versus 0.23 +/- 0.54 for relapse and stone-free). The two groups were otherwise the same. All comparisons used only data obtained prior to relapse. A discriminant function using only these three characteristics correctly identified 72 percent of patients with relapse and 67 percent of those who remained stone-free.

The influence of renal prostaglandins on glomerular filtration rate (GFR) and calcium excretion in urolithiasis

In a clinical study of 275 idiopathic stone formers the GFR was significantly raised in hypercalciuric patients compared with normal controls P less than 0.001). The possibility that the mechanism underlying hypercalciuria and raised GFR may be prostaglandin-mediated was considered because it is now well established that prostaglandins regulate intra-renal haemodynamics and influence tubular electrolyte excretion. Experiments were performed in conscious Sprague Dawley rats to determine the changes in calcium and sodium excretion following prostaglandin synthetase inhibition with indomethacin. Both calcium and sodium excretion together with urine flow were significantly reduced (P less than 0.002). Further experiments were performed in anaesthetised monkeys (Macacca fascicularis) to see if the inhibitory effect of indomethacin was reversible. Exogenous prostaglandin (PGE2) infusion resulted in a marked calciuretic response without producing changes in GFR or blood pressure. Selected hypercalciuric patients were treated with indomethacin, which resulted in a significant fall in urinary calcium excretion (P less than 0.001). This clinical and experimental study suggests that PGE2 is the hormone which determines the renal handling of calcium by controlling renal tubular function.

Long-term persistence of metabolic abnormalities in absorptive or renal hypercalciuria

Seven patients with absorptive hypercalciuria and seven with renal hypercalciuria were re-evaluated 1.67-7.33 years after the original diagnosis. When treatment was temporarily stopped, all showed the same metabolic abnormalities as before: those with absorptive hypercalciuria continued to show increased intestinal absorption of calcium and normal or suppressed parathyroid function, and those with renal hypercalciuria had persistent "renal leak" of calcium and parathyroid stimulation. In view of the persistence of metabolic abnormalities, medical therapy should be regarded as a long-term commitment.

Is there a renal phosphorus leak in recurrent renal stone formers with absorptive hypercalciuria?

In ten male hypophosphataemic hypercalciuric recurrent renal stone formers with absorptive hypercalciuria and ten male normophosphataemic normocalciuric control persons, fasting plasma and urine chemistry was studied throughout the day under basal conditions and following an oral phosphorus load. After overnight fasting, plasma phosphorus and TMP/GFR were lower and urinary calcium higher in patients than in controls. Both in patients and controls, plasma phosphorus rose throughout the morning hours. In the afternoon, plasma phosphorus was almost equal in patients and controls. The circadian rise of plasma phosphorus despite no increase of urinary phosphorus argues against the presence of a fixed renal tubular phosphorus leak in absorptive hypercalciuria, at least in the fasting state. Patients differed from controls not only with respect to urinary calcium, but also with respect to fasting absolute and fractional urinary excretion of sodium and chloride. Increased fractional urinary sodium was found both in normotensive and hypertensive patients. Since tubular reabsorption of phosphorus and the setting of fasting plasma phosphorus depend, among other factors, on tubular handling of sodium, the finding may be relevant for the genesis of transient fasting hypophosphataemia in absorptive hypercalciuria.

Metabolic factors in urolithiasis: a study in Brazil

Clinical and biochemical data were obtained from 50 patients in whom stones form and 20 controls to set up and test a screening procedure for detecting metabolic abnormalities related to the formation of urinary calculi and to provide a preliminary estimate of the frequency of these disorders in our area. A comparison between patients in whom stones form and controls in terms of the quantitative biochemical parameters evaluated (serum calcium, uric acid and inorganic phosphate, and urine calcium, uric acid, inorganic phosphate, oxalic acid, xanthine and alpha-amino-nitrogen) showed a significant difference only with respect to excretion of urinary oxalate by adults, which was higher in patients in whom stones form. Metabolic disorders were detected in 15 adult patients with stones. Of these patients 9 had isolated hyperoxaluria, 3 had incomplete renal tubular acidosis, 1 had idiopathic hypercalciuria, 1 had heterozygous cystinuria and 1 had idiopathic hypercalciuria associated with heterozygous cystinuria. These results suggest a high frequency of metabolic abnormalities in patients in whom stones form in our area, so that the wider use of the screening used here may benefit a large number of patients with preventive and therapeutic measures.

Uric acid saturation in calcium nephrolithiasis

Hyperuricosuria appears to cause calcium oxalate nephrolithiasis by promoting the formation of monosodium urate or uric acid crystals, which either act as seed crystals for calcium oxalate or adsorb normally occurring macromolecular inhibitors of calcium oxalate crystallization. Both mechanisms require that hyperuricosuria cause excessive supersaturation of the urine, but this has not yet been studied under conditions of normal lifestyle. We have measured the saturation with respect to sodium hydrogen urate and the concentration of undissociated uric acid in the urine samples of 67 patients with calcium nephrolithiasis, who had idiopathic hypercalciuria, hyperuricosuria, both, or neither disorder. Patients with hyperuricosuria excreted urine that was supersaturated with respect to monosodium urate or undissociated uric acid more frequently than did other stone formers or normal subjects, and are therefore at a greater risk of forming a solid phase of monosodium urate or uric acid. Treatment measures that lowered uric acid excretion also lowered urine saturation, and this may be the reason that such treatment tends to prevent calcium stone recurrence.

Urine composition in patients with renal stone disease during treatment with allopurinol

Thirty-four male and seven female patients with urolithiasis were treated with 300 mg allopurinol daily for one year in order to prevent stone recurrences. The mean serum-urate concentration in all patients, and the urine urate excretion in patients with a pre-treatment urate excretion above 250 mmol per mol creatinine were significantly reduced. The mean urinary excretion of calcium, magnesium and oxalate was unaffected by the treatment, although six of eight patients with a pre-treatment oxalate excretion above 25 mmol per mol creatinine demonstrated lower urine oxalate values during the treatment. No significant differences were obtained concerning the calcium/magnesium or calcium x oxalate/magnesium x creatinine quotients, but lower values of the calcium x oxalate x urate/magnesium x creatinine2 quotient were observed during allopurinol administration.

Renal transport of oxalate: effects of diuretics, uric acid, and calcium

Clearance experiments were performed in the rat to examine the effects of diuretics on the renal transport of oxalate. In addition, the effect of infusing either uric acid or calcium on the renal transport of oxalate was examined. During control periods, the fractional excretion of oxalate (FEOx) averaged 118.0 +/- 2.1%. Acute administration of either chlorothiazide, furosemide, or indanyl-oxyacetic acid (MK-196), a new uricosuric diuretic, resulted in a significant decrease in the FEOx in all groups to 104.8 +/- 2.4%, 111.3 +/- 2.1%, and 108.6 +/- 2.7%, respectively. Infusion of uric acid increased urinary uric acid excretion from 2.41 +/- 0.28 to 4.26 +/- 0.03 micrograms/min/g kidney wt (P less than 0.001) and decreased FEOx to 104.0 +/- 2.4% (P less than 0.001 compared to control). Infusion of calcium chloride increased urinary calcium excretion from 0.10 +/- 0.04 to 0.44 +/- 0.06 micrograms/min/g kidney wt (P less than 0.001) but had no effect on the FEOx which averaged 118.3 +/- 8.3% (P = NS compared to control). These studies show that the acute administration of chlorothiazide, furosemide, or MK-196, as well as increasing urinary uric acid excretion by uric acid infusion, are all associated with a decrease in the FEOx. Acutely increasing urinary calcium excretion, however, had no effect on oxalate transport.

Renal stones in Wilson's disease

Fifty-four patients with Wilson's disease were studied with regard to renal stones. Seven of the 45 patients (16 per cent) who underwent roentgenographic procedures of the urinary tract had unequivocal evidence of renal stones. In four of the seven patients with Wilson's disease who had renal stones, the stones were discovered at the time or before the diagnosis of Wilson's disease was made. Of the several possible factors that may predispose patients with Wilson's disease to renal stone formation, the renal tubular acidosis pattern of abnormality in acid-base excretion is probably the most significant. In general, patients with renal stones and unexplained neurologic, bony or hepatic abnormalities should be screened for Wilson's disease by slit-lamp examination, determination of serum copper and ceruloplasmin concentrations, and urinary excretion of copper, particularly if they have relatively alkaline urine.

Effects of different diuretics on urinary calcium excretion in a general population

Calcium excretion by users and non-users of thiazide diuretics and frusemide was studied during a health survey. Men taking thiazides excreted less calcium than age- and weight-matched controls. Both men and women taking thiazides excreted less calcium relative to sodium than controls. Women taking thiazides excreted significantly less calcium than women taking frusemide. Both men and women taking thiazides excreted less calcium relative to creatinine than sex-matched groups taking frusemide.

Inhibitors and promoters of stone formation

The understanding of the formation of urinary stones centers around three main mechanisms: the urinary concentration of stone-forming ions, the role of promoters, and the role of inhibitors of crystal formation and crystal aggregation. With respect to the promoting activity, lately emphasis has shifted from the role of the organic matrix to that of one salt inducing by epitaxy the precipitation of another salt. Among the inhibitors, it has become necessary to distinguish between those affecting crystal formation and those affecting crystal aggregation. For measuring the inhibitory activity, the various techniques and their relevance have been reviewed. It has been found that the main inhibitors for calcium phosphate and calcium oxalate precipitation are citrate, pyrophosphate, and perhaps magnesium. Those for calcium phosphate and calcium oxalate aggregation are glycosaminoglycans, pyrophosphate, and citrate. Among the synthetic inhibitors, the diphosphonates are the most powerful for both processes. The role and the therapeutic implications of these various concepts have been discussed.

Prevention of calcium stones with thiazides

On the basis of almost 15 years of experience with thiazide treatment in 346 patients with calcium stones, we believe that the following conclusions are justified: 1) Stone progression ceases in at least 90% of patients who take hydrochlorothiazide (50 mg, twice daily) on a regular basis. 2) A reduced dose of hydrochlorothiazide, i.e., 25 mg twice daily, appears to be effective in a significant proportion of patients. 3) Thiazides are effective in normocalciuric as well as hypercalciuric patients and in most patients with tubular ectasia (medullary sponge kidney). 4. Side effects necessitate discontinuation of thiazide treatment in approximately 7% of patients. The incidence and severity of side effects is reduced by initiating treatment with a small dose and by increasing the dose progressively until the full maintenance dose is achieved. A trial with a reduced dose is warranted in patients who are unable to tolerate the regular maintenance dose. 5) The therapeutic efficacy of thiazides in stone prevention cannot be accurately predicted by the degree of hypocalciuric response. Stone prevention may cease despite a minimal hypocalciuric response, whereas stone progression may occur when an adequate hypocalciuric response has taken place. 6) In addition to the hypocalciuric action, thiazides reduce urine oxalate excretion and increase urine zinc and (probably) magnesium; these effects probably contribute to the efficacy of this agent in stone prevention.

Adsorption of heparin on sodium acid urate

The adsorption of heparin on sodium acid urate powder suspended in aqueous solution was found to be dependent upon the concentration of Ca2+ and Mg2+. It was concluded that heparin adsoprtion on sodium acid urate powder can occur in urine. Speculations are made about the relevance of these observations to calcium oxalate urolithiasis.

Experience with the radioimmunoassay for parathyroid hormone in the diagnosis of primary hyperparathyroidism

Our results with radioimmunoassay studies for parathyroid hormone performed during the last 6 years are compared retrospectively to results of the laboratory tests customarily secured when hyperparathyroidism is suspected. The results obtained in patients with known primary hyperparathyroidism and in patients with unconfirmed but presumptive hyperparathyroidism are compared to the results obtained from a group of normal controls. Despite the fact that certain discrepant results were noted in the earlier assay techniques the over-all results and, in particular, those of more recent years have been highly sensitive and reproducible corroboratives of the existence of primary hyperparathyroidism. About two-thirds of the patients with primary hyperparathyroidism will present to the urologist. All patients with calcium-containing stones should have at least 3 determinations of the serum calcium in screening for primary hyperparathyroidism. The radioimmunoassay for parathyroid hormone provides the most reliable confirmation. The patient with calculous disease, elevation of the immunoreactive parathyroid hormone level and hypercalcemia is virtually certain to have primary hyperparathyroidism.

Renal acidifying ability in subjects with recurrent stone formation

To determine the incidence of an acidification defect in men in whom calcium stones form and its relationship to parathyroid function 120 such patients were given an acute dosage of 0.1 gm. per kg. oral ammonium chloride and circulating immunoreactive parathyroid hormone was determined. The subjects were divided into 2 groups, according to normal or high parathormone levels. Group 1 consisted of 46 men in whom immunoreactive parathyroid hormone was less than or equal to 60 mulEq. per ml. and group 2 consisted of 74 men with immunoreactive parathyroid hormone greater than 60 mulEq. per ml. Of 8 men in whom the urine failed to acidify to less than a pH of 5.3, 3 were from group 1 and 5 were from group 2. None of the patients had an active urinary tract infection. There was no difference in minimal urine pH among the patients in whom the urine acidified normally regardless of immunoreactive parathyroid hormone. The incidence of abnormal acidification in our population was 6% and all of these patients had the incomplete form of renal tubular acidosis. These findings have important therapeutic implications.

Urolithiasis associated with hypercalciuria

Fifty male patients with urolithiasis (UL), associated with idiopathic hypercalciuria (IH), were studied in comparison to a group of 18 male normocalcemic patients with inactive calcium stone disease of unknown etiology. In the group of IH-UL, in addition to hypercaliuria, statistically significant hyperphosphaturia with decreased tubular reabsorption of phosphate and hyperuricemia were observed; there was a tendency to hypophosphatemia although non-significant. In 36% of the IH-UL patients the first episode of renal colic appeared at age 40 to 50. Thirty-eight per cent of the IH-UL patients had recurrent stone formation. Twenty per cent of the IH-UL patients had a family history of urolithiasis. Forty-six per cent of all stones contained oxalate in addition to calcium, and 25% of the stones contained oxalate and phosphate.

Placebo versus allopurinol for renal calculi

Certain patients with recurrent calcium oxalate calculi will show a mild uricacidemia and/or uricosuria. A prospective blind study was begun in 1970, comparing placebo to allopurinol in the management of these patients. The 92 patients had been followed for a minimum of 6 months to 5 years before the code was broken. It is demonstrated clearly that there is a placebo effect in the management of renal calculous disease. It also has been shown that the only event that clearly separates the 2 groups is complete cessation of calculous formation. Allopurinol is effective in 61 per cent of the patients and these successes usually can be identified after 1 year of treatment.

Effect of hydrochlorothiazide therapy on the crystallization of calcium oxalate in urine

The effect of hydrochlorothiazide on the formation of renal stones was evaluated by quantitative assessment of the propensity of urine to undergo crystallization of calcium oxalate. In seven patients with calcium urolithiasis (three with absorptive hypercalciuria, one with renal hypercalciuria, and three with normocalciuric nephrolithiasis), the urinary activity product ratio and formation product ratio of calcium oxalate were measured both on and off therapy with hydrochlorothiazide (50 mg orally twice a day). The activity product ratio (state of saturation with respect to calcium oxalate) decreased in the majority of cases, primarily as a result of the fall in urinary calcium. The formation product ratio (limit of metastability) increased in all cases; the cause of the increase was not readily apparent. Both changes reduced the propensity of urine to undergo crystallization of calcium oxalate, and therefore may account for the clinical improvement reported during thiazide therapy in nephrolithiasis.