The risk of renal stone formation during and after long duration space flight

BACKGROUND: The formation of a renal stone during space flight may have serious negative effects on the health of the crewmember and the success of the mission. Urinary biochemical factors and the influence of dietary factors associated with renal stone development were assessed during long duration Mir Space Station missions. METHODS: Twenty-four-hour urine samples were collected prior to, during and following long duration space flight. The relative urinary supersaturation of calcium oxalate, calcium phosphate (brushite), sodium urate, struvite and uric acid were determined. RESULTS: Changes in the urinary biochemistry of crewmembers during long duration spaceflight demonstrated increases in the supersaturation of the stone-forming salts. In-flight hypercalciuria was evident in a number of individual crewmembers and 24-hour dietary fluid intake and urine volume were significantly lower. During flight, there was a significant increase in brushite supersaturation. CONCLUSIONS: These data suggest acute effects of space flight and postflight changes in the urinary biochemistry favoring increased crystallization in the urine. The effects of dietary intake, especially fluid intake, may have a significant impact on the potential for renal stone formation. Efforts are now underway to assess the efficacy of a countermeasure to mitigate the increased risk.     

Comparison of renal function and metabolic abnormalities of cystine stone patients and calcium oxalate stone patients in China

Purpose

To compare renal function and metabolic abnormalities of cystine stone patients and calcium oxalate stone patients in China.

Methods

Between 2008 and 2011, thirty cystine stone patients were involved in our study, and an equal number of age- and gender pair-matched patients with calcium oxalate stones. Non-stone forming individuals were elected as controls. The evaluation included blood chemistry studies and 24-h urine collection in both groups of patients.

Results

The cystine stone patients had higher mean values of serum blood urea nitrogen, urate and creatinine levels than patients in other two groups. With respect to urine risk factors, cystine stone patients had higher urinary citrate and lower urinary oxalate and creatinine than calcium oxalate stone patients. When compared to non-stone forming individuals, cystine stone patients had higher urinary urate excretion and lower urinary creatinine excretion. Metabolic abnormalities could be demonstrated in 80 % of the cystine stone patients and in 100 % of the calcium oxalate stone patients. We also compared urine risk factors among cystine stone patients with different urine cystine excretion (<1 mmol/24 h, 1–2 mmol/24 h and >2 mmol/24 h). No significant difference was found in urine risk factors among three groups.

Conclusions

This study suggested that cystine stone patients were at greater risk for the loss of renal function than calcium oxalate stone patients, but the risk of the formation of calcium oxalate stones was lower. Our results also indicated that urinary cystine had little or no impact on the excretion of urine chemistries in cystine stone patients.     

Bone metabolism and renal stone risk during International Space Station missions

Bone loss and renal stone risk are longstanding concerns for astronauts. Bone resorption brought on by spaceflight elevates urinary calcium and the risk of renal stone formation. Loss of bone calcium leads to concerns about fracture risk and increased long-term risk of osteoporosis. Bone metabolism involves many factors and is interconnected with muscle metabolism and diet. We report here bone biochemistry and renal stone risk data from astronauts on 4- to 6-month International Space Station missions. All had access to a type of resistive exercise countermeasure hardware, either the Advanced Resistance Exercise Device (ARED) or the Interim Resistance Exercise Device (iRED). A subset of the ARED group also tested the bisphosphonate alendronate as a potential anti-resorptive countermeasure (Bis + ARED). While some of the basic bone marker data have been published, we provide here a more comprehensive evaluation of bone biochemistry with a larger group of astronauts. Regardless of exercise, the risk of renal stone formation increased during spaceflight. A key factor in this increase was urine volume, which was lower during flight in all groups at all time points. Thus, the easiest way to mitigate renal stone risk is to increase fluid consumption. ARED use increased bone formation without changing bone resorption, and mitigated a drop in parathyroid hormone in iRED astronauts. Sclerostin, an osteocyte-derived negative regulator of bone formation, increased 10–15% in both groups of astronauts who used the ARED (p < 0.06). IGF-1, which regulates bone growth and formation, increased during flight in all 3 groups (p < 0.001). Our results are consistent with the growing body of literature showing that the hyper-resorptive state of bone that is brought on by spaceflight can be countered pharmacologically or mitigated through an exercise-induced increase in bone formation, with nutritional support. Key questions remain about the effect of exercise-induced alterations in bone metabolism on bone strength and fracture risk.     

THE INTERRELATIONSHIP OF CALCIUM AND MAGNESIUM ABSORPTION IN IDIOPATHIC HYPERCALCIURIA AND RENAL CALCIUM STONE DISEASE

Purpose

A decreased concentration of magnesium in the urine is a risk factor for renal calcium stone disease that may be caused by decreased enteral absorption of magnesium. We analyze the possible reciprocal influences of enteral absorption of calcium and magnesium in patients with renal stone disease.

Materials and Methods

We measured the fractional enteral absorption of sup 47 calcium and²⁸magnesium in 11 patients with renal calcium stone disease, including 8 with and 3 without hypercalciuria. Two tests were performed using calcium and magnesium, respectively, followed by another test in which the enteral absorption of calcium and magnesium was measured after both cations were administered together.

Results

We noted no clear influence of either cation on the absorption of the other in the 3 patients without hypercalciuria. However, in the 8 hypercalciuric patients enteral calcium absorption decreased after the concurrent administration of magnesium and enteral magnesium absorption increased after the concurrent administration of calcium. Each effect was proportional to the other.

Conclusions

The results of this study indicate that the oral supplementation of magnesium in patients with hyperabsorptive hypercalciuria and renal calcium stone disease is favorable because it decreases calcium absorption and increases magnesium absorption. Both factors may reduce risk factors for renal calcium stone formation.     

METABOLIC URINARY CORRELATES OF CALCIUM OXALATE DIHYDRATE IN RENAL STONES

Purpose

We determined what metabolic features of the 24-hour urine predict calcium oxalate dihydrate in kidney stones. Prior studies have suggested that low urine magnesium, high urine calcium, high calcium-to-oxalate ratio and high urine supersaturation with respect to calcium oxalate monohydrate predict calcium oxalate dihydrate.

Materials and Methods

Stone analyses and results from 2, 24-hour pretreatment urine collections from 96 patients with nephrolithiasis were drawn from 3 kidney stone prevention centers. Standard stone risk measurements were made on the urine, including supersaturation for calcium oxalate monohydrate, brushite and uric acid.

Results

The main differences in metabolic urine findings were between patients with no calcium oxalate dihydrate and those with any calcium oxalate dihydrate in stones. Percent calcium oxalate dihydrate itself did not correlate with urine findings. Patients with no calcium oxalate dihydrate in stones showed a biphasic pattern of urine calcium oxalate monohydrate supersaturation, about half had values below almost any found among patients with calcium oxalate dihydrate in stones (less than 7) and the rest overlapped with the calcium oxalate dihydrate group. Except for higher calcium oxalate monohydrate supersaturation, patients with calcium oxalate dihydrate in stones had higher urine calcium excretion and lower urine citrate concentrations, even after calcium oxalate monohydrate supersaturation was considered.

Conclusions

Patients with low calcium oxalate monohydrate supersaturation (less than 7) are unlikely to have calcium oxalate dihydrate in renal stones. However, many patients with no calcium oxalate dihydrate have higher calcium oxalate monohydrate supersaturation values, and so prediction of calcium oxalate dihydrate or its absence from urine findings is imperfect. Urine magnesium and the calcium-to-oxalate ratio are unrelated to calcium oxalate dihydrate.     

Renal stone risk in a simulated microgravity environment: impact of treadmill exercise with lower body negative pressure

PURPOSE: Prolonged exposure to microgravity during spaceflight causes metabolic changes that increase the risk of renal stone formation. Studies during the Gemini, Apollo, Skylab and Shuttle missions demonstrated alterations in renal function, fluid homeostasis and bone resorption that result in increased urinary supersaturation of calcium oxalate, brushite, sodium urate and uric acid. Developing countermeasures to increased urinary supersaturation is an important priority as the duration of space missions increases. MATERIALS AND METHODS: A total of 11 sets of identical twins remained on 6-degree head down, tilt bed rest for 30 days to simulate prolonged microgravity. One twin per pair was randomly selected to exercise while supine in a lower body negative pressure chamber 6 days weekly for 40 minutes, followed by 5 minutes of resting lower body negative pressure at 50 mm Hg. The other twin served as a nonexercise control. Pressure in the exercise lower body negative pressure chamber (52 to 63 mm Hg) was adjusted to produce footward forces equivalent to those for upright running on Earth at 1.0 to 1.2 x body weight. Pre-bed rest urinary stone risk profiles were done elsewhere after 5 days of a standardized diet, consisting of 170 mEq sodium, 1,000 mg calcium, 0.8 gm/kg animal protein and 2,500 kcal, and then throughout the bed rest and recovery phases of the protocol. RESULTS: A significant increase in urinary calcium after just 1 week of bed rest was noted in the nonexercise control group (p = 0.001). However, no such increase was noted in the exercise group. Brushite supersaturation increased significantly from bed rest in each group, although the increase was significantly higher in the nonexercise control group than in the exercise group (p = 0.006). Calcium oxalate supersaturation increased during bed rest in the exercise group (p = 0.004). It trended toward a higher level in the nonexercise control group, although this did not achieve significance (p = 0.055) Mean urine volume +/- SD was significantly higher in the nonexercise control group than in the exercise group at bed rest week 2 and at week 3 (2.01 +/- 0.21 vs 1.63 0.18 l and 2.03 +/- 0.22 vs 1.81 +/- 0.20, respectively). Urinary pH was significantly higher in the nonexercise control group than in the exercise group at week 1 and week 3 (6.62 +/- 0.7 vs 6.49 +/- 0.5 and 6.58 +/- 0.6 vs 6.49 +/- 0.8, respectively, p = 0.01). CONCLUSIONS: Bed rest significantly alters the urinary environment to favor calculous formation. Lower body negative pressure chamber treadmill exercise offers some protection against increases in stone risk during simulated microgravity, particularly with regard to the risks of hypercalciuria and brushite stone formation. The use of lower body negative pressure to augment aerobic exercise in space may decrease the risk of stone formation in astronauts. Adjunct measures, including aggressive hydration and alkalinization therapy, should be considered.     

SUPERSATURATION AND STONE COMPOSITION IN A NETWORK OF DISPERSED TREATMENT SITES

Purpose

We determined the validity of urine supersaturation assessed from 2, 24-hour urine collections from outpatients eating uncontrolled diets and receiving care at a network of treatment sites that uses a central laboratory. We compared supersaturation to stone composition to determine whether supersaturation values correlate with composition.

Materials and Methods

Two 24-hour urine samples collected from 183 patients at 6 treatment sites were shipped to a single central laboratory. Complexations and crystallizations in vitro from aging during the transport step were interrupted by pH change in acid and alkaline directions. Relevant analytes were measured, and supersaturation was calculated for calcium oxalate, calcium phosphate as brushite and uric acid. Stone analysis was done at various laboratories.

Results

Urine supersaturation values correlated well with stone composition. Higher calcium phosphate and uric acid supersaturation was noted when stones contained higher amounts of calcium phosphate and any uric acid, respectively. In a validation study values of relevant urine materials were unchanged after 48 hours of aging.

Conclusions

Despite the need for sample transport, resulting in the inevitable aging of samples, and variations in diet and details of sample collection, supersaturation values measured in only 2, 24-hour urine collections accurately reflected stone composition. This finding indicates that supersaturation values are reasonably stable in most patients during the months to years required for stones to form. In addition, samples collected in standard practice settings and sent to a central laboratory may accurately reflect these supersaturation values.     

Effect of potassium depletion on urinary stone risk factors in Wistar rats

Various studies have suggested that potassium depletion leads to acidosis and hypocitraturia. In Northeastern Thailand, for example, mild hypokalemia and mild hyperoxaluria are observed in most stone formers. However, there are limited reports about the direct link between potassium depletion and the formation of urinary stones, most of which are calcium oxalate stones. Therefore, we studied the direct effect of potassium depletion on the risk factors for calcium oxalate stone formation. Seventy-two rats were fed a control diet or a potassium-deficient diet for 1, 2, or 3 weeks (n = 12 per group). Twenty-four-hour urine collection was done for the measurement of potassium, calcium, oxalate, glycolate, citrate, phosphorus, and magnesium. Lactate dehydrogenase activity was also measured in order to assess renal tubular damage, and kidneys were harvested for histological examination. Furthermore, urinary supersaturation of calcium oxalate was calculated. With potassium depletion, the urinary concentrations of potassium, citrate, magnesium, and phosphorus decreased rapidly. There was no detectable renal damage, renal calcium deposition, and no significant increase of urinary oxalate or calcium. However, the urinary supersaturation index of calcium oxalate increased significantly in rats with potassium depletion. These findings indicate that potassium deficiency may increase the risk of stone formation through enhanced supersaturation.     

Long-Term Incidence and Risks for Recurrent Stones Following Contemporary Management of Upper Tract Calculi in Patients with a Urinary Diversion

Purpose

The long-term rate of stone recurrence following contemporary minimally invasive management of calculi was determined in patients with urinary diversion and to identify specific risk factors for these recurrences.

Materials and Methods

We followed for a minimum of 12 months 25 patients (29 renal units) with upper tract calculi associated with urinary diversion, and treated with extracorporeal shock wave lithotripsy and/or percutaneous nephrostolithotomy. The risk of recurrent stones at 5 years was determined by a Kaplan-Meier estimate, while potential risk factors for recurrence were analyzed using a log-rank comparison.

Results

Stones recurred in 8 patients (32 percent) 18 to 61 months (mean 27.0) after treatment. The risk of new stone formation after 5 years was estimated to be 63.3 percent and was significantly greater in patients with recurrent bacteriuria after treatment. Neither stone history, type of procedure used, stone composition nor radiographic status of completion of treatment significantly influenced this risk.

Conclusions

Contemporary management of upper tract calculi in patients with a urinary diversion is associated with a high recurrence rate, especially among those with recurrent bacteriuria, regardless of whether the patient is initially rendered stone-free. Continued close surveillance and antibiotic prophylaxis seem to be essential in this high risk patient population.     

Urinary Calculi as a Late Complication of the Indiana Continent Urinary Diversion: Comparison with the Kock Pouch Procedure

Purpose

Although urinary calculi have been frequent late complications of the Kock continent urinary diversion, they have not been regarded as significant problems in patients with the Indiana pouch because of the lack of foreign material present. However, stones developed in a significant percentage of our patients with an Indiana pouch. We investigated the characteristics of stone formation in patients with the Indiana pouch and compared them to those with a Kock pouch.

Materials and Methods

Detailed clinical courses regarding stone formation were reviewed in 72 patients with a Kock pouch and 54 with an Indiana pouch who had a minimum followup of 12 months.

Results

Stones developed in 7 of 54 patients (12.9 percent) with an Indiana pouch compared to 31 of 72 (43.1 percent) with a Kock pouch. The incidence gradually increased with longer followup but it was lower in the Indiana than in the Kock pouch group (5-year stone-free rate 84 percent versus 66 percent, respectively). Although the stones consisted principally of a mixture of struvite, carbonate apatite and ammonium hydrogen urate, variable amounts of calcium oxalate were identified in 50 percent of the Indiana pouch calculi.

Conclusions

Not only urinary infections but also metabolic factors were considered to be involved in stone formation within the Indiana pouch. However, the substantially higher rate of stone formation in our Kock and Indiana pouch groups than has been reported in the United States suggested that no or infrequent pouch irrigations in our patients were important risk factors for urinary calculi.     

Updates in the Metabolic Management of Calcium Stones

Purpose of Review

Urinary risk factors, such as hypercalciuria, hypocitraturia, and hyperoxaluria, either in combination or alone, are associated with calcium stones. Dietary habits as well as underlying medical conditions can influence urinary risk factors. Evaluation of the conglomerate of patients’ stone risks provides evidence for individualized medical management, an effective and patient-supported approach to prevention.

Recent Findings

Many patients with stones desire prevention to avoid repeated surgical interventions. Yet, recent practice pattern assessments and health care utilization data show that many patients are rarely referred for metabolic evaluation or management. Innovations in metabolic management over the past decade have improved its effectiveness in reducing risk and preventing calcium stones. Although no new pharmacologic agents for calcium stone prevention have recently become available, there is relatively new thinking about some diet-based approaches.

Summary

This review will synthesize current evidence to support individualized metabolic management of calcium stones.

     

ENDOSCOPIC MAPPING OF RENAL PAPILLAE FOR RANDALL''S PLAQUES IN PATIENTS WITH URINARY STONE DISEASE

Purpose

Papillary "Randall's plaques" are theorized to act as nidi for urinary stone formation. The aim of this study was to document the presence, pattern and distribution of Randall's plaques in patients undergoing endoscopic procedures for urinary stone disease.

Materials and Methods

Patients undergoing either ureteroscopy or percutaneous nephroscopy for removal of urinary stones underwent endoscopic mapping of accessible calices. These patients were compared to a smaller group of patients undergoing endoscopic procedures for conditions unrelated to urinary stone disease. In patients found to have papillary plaques the presence, location and pattern of plaques were recorded. Plaque formation was correlated with patient age and sex, and primary composition of extricated stone.

Results

Endoscopic evidence of papillary Randall's plaques was found in 74% of 57 patients having ureteroscopic (21) or percutaneous (36) stone removal. Of 7 patients having endoscopic procedures for conditions unrelated to urinary stone disease 3 (43%) had evidence of papillary plaques. Plaques were found uniformly throughout all calices and most commonly diffusely scattered over the papillary surface. There was no correlation between patient age or sex and the presence of plaques. The incidence of plaques varied with the primary composition of extracted stones, and was 100% for calcium phosphate and uric acid, 88% for calcium oxalate, 33% for cystine and 20% for struvite. The incidence of papillary plaques was significantly more common in patients with calcium oxalate (88 versus 43%, p = 0.023) and calcium phosphate stones (100 versus 43%, p = 0.009) than patients without a history of urinary stone disease.

Conclusions

The endoscopic incidence of papillary Randall's plaques in patients with urolithiasis varies with the primary composition of formed urinary stones. Randall's plaques are found in the majority of patients with calcium urinary stone disease. Our findings suggest that the presence of papillary plaques is associated with calcium nephrolithiasis and may contribute to the pathogenesis of calcium urinary stones.     

Influence of cranberry juice on the urinary risk factors for calcium oxalate kidney stone formation

Cranberry juice is popular remedy for many ills; apart from the pleasant tasting many people drink it to help in preventing UTIs and stones. Authors from Cape Town (where there is the added benefit of an excellent climate) assessed the influence of cranberry juice on urinary risk factors for calcium oxalate calculi in a randomized crossover trial, showing that it has anti‐lithogenic properties. In the second paper, authors from Jerusalem report on 14 patients with distal ureteric strictures after kidney transplantation, all of whom were treated endourologically. They found transurethral incision of the distal ureteric stricture to be effective.

OBJECTIVE

To investigate the potential influence of cranberry juice on urinary biochemical and physicochemical risk factors associated with the formation of calcium oxalate kidney stones, as this product might affect the chemical composition of urine.

SUBJECTS AND METHODS

Urinary variables were assessed in a randomized cross‐over trial in 20 South African men (students) with no previous history of kidney stones. The first group of 10 subjects drank 500 mL of cranberry juice diluted with 1500 mL tap water for 2 weeks, while the second group drank 2000 mL of tap water for the same period. This was followed by a 2‐week ‘washout’ period before the two groups crossed over. During the experimental phase subjects kept a 3‐day food diary to assess their dietary and fluid intakes; 24‐h urine samples were collected at baseline and on day 14 of the trial periods, and analysed using modern laboratory techniques. Urine analysis data were used to calculate the relative urinary supersaturations of calcium oxalate, uric acid and calcium phosphate. Data were assessed statistically by analysis of variance.

RESULTS

The ingestion of cranberry juice significantly and uniquely altered three key urinary risk factors. Oxalate and phosphate excretion decreased while citrate excretion increased. In addition, there was a decrease in the relative supersaturation of calcium oxalate, which tended to be significantly lower than that induced by water alone.

CONCLUSION

Cranberry juice has antilithogenic properties and, as such, deserves consideration as a conservative therapeutic protocol in managing calcium oxalate urolithiasis.

     

Men and Women in Space: Bone Loss and Kidney Stone Risk After Long‐Duration Spaceflight

Bone loss, a key concern for long‐duration space travelers, is typically considered a female issue. The number of women who have flown long‐duration space missions is now great enough to allow a quantitative comparison of changes in bone and renal stone risk by sex. Participants were 42 astronauts (33 men and 9 women) on long‐duration missions to the International Space Station. Bone mineral density (by dual‐energy X‐ray absorptiometry) and biochemical markers of bone metabolism (from blood and urine samples) were evaluated before and after flight. Data were analyzed in two groups, based on available resistance exercise equipment. Missions were 49 to 215 days in duration, flown between 2000 and 2012. The bone density response to spaceflight was the same for men and women in both exercise groups. The bone mineral density response to flight was the same for men and women, and the typical decrease in bone mineral density (whole body and/or regional) after flight was not observed for either sex for those using an advanced resistive exercise device. Biochemical markers of bone formation and resorption responded similarly in male and female astronauts. The response of urinary supersaturation risk to spaceflight was not significantly different between men and women, although risks were typically increased after flight in both groups, and risks were greater in men than in women before and after flight. The responses of men and women to spaceflight with respect to these measures of bone health were not different. © 2014 American Society for Bone and Mineral Research.     

A STUDY OF DIETARY CALCIUM AND OTHER NUTRIENTS IN IDIOPATHIC RENAL CALCIUM STONE FORMERS WITH LOW BONE MINERAL CONTENT

Purpose

Patients with calcium renal stone are reported to have lower bone mineral density. The state of bone density in patients with renal stones have different explanations but the role of nutritional factors seems to be crucial. A group of 48 consecutive male calcium renal stone formers was studied to investigate the relationship between bone density and dietary intake.

Materials and Methods

Patients completed a dietary diary for a 3-day period during normal diet. Nutrients and calories were calculated by food composition tables using a computerized procedure. Bone densitometry was assessed at the lumbar spine and femoral neck, and expressed as Z score. A blood sample was collected and was analyzed for serum biochemistry including alkaline phosphatase, parathyroid hormone and 1,25 vitamin D. A 24-hour urine sample was analyzed for calcium, phosphate oxalate, citrate and other electrolytes.

Results

Dietary calcium intake was significantly lower (p <0.01) in patients with low than in those with normal bone mineral density. There was no difference in serum parathyroid hormone levels, phosphate and alkaline phosphatase between the 2 groups. The results suggest that some renal stone formers seem to be unable to decrease renal excretion of calcium on a low calcium diet leading to a negative calcium balance.

Conclusions

A primary abnormality of bone metabolism could be a reasonable explanation of reduced bone density observed in renal stone formers on a low calcium diet since serum parathyroid hormone levels are in the normal range. From a therapeutic point of view these data confirm that restriction of dairy products in renal stone formers should be avoided.     

Bisphosphonates as a supplement to exercise to protect bone during long-duration spaceflight

Summary

We report the results of alendronate ingestion plus exercise in preventing the declines in bone mass and strength and elevated levels of urinary calcium and bone resorption in astronauts during 5.5 months of spaceflight.

Introduction

This investigation was an international collaboration between NASA and the JAXA space agencies to investigate the potential value of antiresorptive agents to mitigate the well-established bone changes associated with long-duration spaceflight.

Methods

We report the results from seven International Space Station (ISS) astronauts who spent a mean of 5.5 months on the ISS and who took an oral dose of 70 mg of alendronate weekly starting 3 weeks before flight and continuing throughout the mission. All crewmembers had available for exercise a treadmill, cycle ergometer, and a resistance exercise device. Our assessment included densitometry of multiple bone regions using X-ray absorptiometry (DXA) and quantitative computed tomography (QCT) and assays of biomarkers of bone metabolism.

Results

In addition to pre- and post-flight measurements, we compared our results to 18 astronauts who flew ISS missions and who exercised using an early model resistance exercise device, called the interim resistance exercise device, and to 11 ISS astronauts who exercised using the newer advanced resistance exercise device (ARED). Our findings indicate that the ARED provided significant attenuation of bone loss compared with the older device although post-flight decreases in the femur neck and hip remained. The combination of the ARED and bisphosphonate attenuated the expected decline in essentially all indices of altered bone physiology during spaceflight including: DXA-determined losses in bone mineral density of the spine, hip, and pelvis, QCT-determined compartmental losses in trabecular and cortical bone mass in the hip, calculated measures of fall and stance computed bone strength of the hip, elevated levels of bone resorption markers, and urinary excretion of calcium.

Conclusions

The combination of exercise plus an antiresoptive drug may be useful for protecting bone health during long-duration spaceflight.     

Urinary phytate in calcium oxalate stone formers and healthy people--dietary effects on phytate excretion

The phytate urinary levels in a group of active calcium oxalate stone formers were studied and compared with those found in healthy people. Urinary phytate was significantly lower for stone formers. If deficit of the capacity to inhibit crystallization of calcium salts is considered an important factor related to calcium stone formation, the excretion of low phytate amounts could be an important risk factor in the development of this type of renal calculi. The influence of dietary phytate on urinary excretion was also studied. Clearly maintenance of a phytate-free diet significantly decreased the urinary excretion of phytate (about 50% after 36 h). This demonstrated the importance of dietary phytate in maintaining adequate urinary levels to permit effective crystallization inhibition of calcium salts and consequently preventing renal stone development.     

The influence of a high-oxalate/low-calcium diet on calcium oxalate renal stone risk factors in non-stone-forming black and white South African subjects

OBJECTIVE: To evaluate the influence of a high-oxalate/low-calcium diet on calcium oxalate stone risk factors in both black South Africans (who are largely immune to kidney stones) and white South Africans (in whom stones are more common). SUBJECTS AND METHODS: Urinary and dietary variables were examined in 11 black and 11 white South African men. None of the subjects had had a kidney stone or any metabolic illness. Their normal domestic food intake was assessed using a semiquantitative food frequency questionnaire. Subjects were given a standardized high-oxalate/low-calcium diet for 3 days; 24-h urine samples were collected before the protocol and during the final day. The samples were analysed using routine modern laboratory techniques. The urine analysis data were used to calculate the Tiselius risk index and the relative urinary supersaturations of calcium oxalate, uric acid and calcium phosphate. RESULTS: Urine analysis showed an intriguing anomaly; black subjects had significantly higher urinary pH and oxalate values than whites (6.50 vs 6.21 and 0.23 vs 0.14 mmol/24 h, respectively), while their urinary citrate was lower (1.47 vs 3.69 mmol/24 h). In addition, the Tiselius risk index and relative supersaturation of calcium oxalate were higher in black subjects. These results are contrary to those which might have been reasonably expected when comparing stone-free and stone-prone groups. After the dietary protocol, the only urinary variable which changed significantly was urinary oxalate, which increased by 57% in whites. CONCLUSION: Factors which are conventionally used to assess stone risk (pH, oxaluria, citraturia, relative supersaturation) are not helpful in identifying why South African blacks are relatively immune to stones. We suggest that relatively lower oxalate absorption rates may be a physiological feature of this racial group.     

Urinary citrate excretion in healthy children depends on age and gender

Background

Hypocitraturia is considered a major risk factor for calcium stone formation. However, there is no widely accepted reference database of urinary citrate excretion in children. The aim of our study was to determine the amount of citrate eliminated in the urine over a 24-h period in a pediatric cohort and to determine an optimal unit reflecting excretion.

Methods

The study cohort comprised 2,334 healthy boys and girls aged 2–18 years. The levels of urinary citrate were assessed by an enzymatic method in 24-hour urine and expressed in absolute values, as urinary concentration, citrate/creatinine ratio, per kilogram of body weight, in relation to 1.73 m², and as the calcium/citrate index.

Results

Similar incremental age-related citraturia rates were observed in both male and female subjects until puberty during which time citrate excretion became significantly higher in girls. Urinary citrate adjusted for creatinine and for body weight showed a significantly decreasing trend with increasing age in both sexes. Urinary citrate corrected for body surface was weakly correlated with age. Thus, the assumption of 180 mg/1.73 m²/24 h for males and 250 mg/1.73 m²/24 h for females as lower cut-off values appeared to be reliable from a practical perspective.

Conclusions

We found distinct sex-dependent differences in citraturia at the start of puberty, with significantly higher values of urinary citrate in girls than in boys. Further prospective studies are warranted to elucidate whether this difference represents a differentiated risk of urolithiasis.     

COMPARATIVE STUDY OF THE INFLUENCE OF 3 TYPES OF MINERAL WATER IN PATIENTS WITH IDIOPATHIC CALCIUM LITHIASIS

Purpose

While there is general agreement on the need to increase urinary volume in stone formers, contrasting opinions have been expressed about the hardness of water and stone incidence. We evaluate the influence of 3 types of mineral water on urinary analytes in 22 idiopathic calcium oxalate stone formers.

Materials and Methods

All patients underwent a nutritional and metabolic evaluation at baseline, and after a controlled diet including water with a high, medium or low calcium content.

Results

In patients who drank water with high and medium calcium contents calcium excretion increased, although the results did not reach statistical significance. In those who drank water with the highest calcium content oxalate excretion significantly decreased (p = 0.05), as did the oxalate-to-calcium ratio (p = 0.05). Moreover, these modifications did not induce relevant changes in urinary saturation. In patients who drank water with the greatest amount of bicarbonate citrate excretion increased (p = 0.03).

Conclusions

Mineral water with a higher calcium content induced increased calcium excretion but significantly decreased oxalate excretion. These data are in accordance with those of others, who did not find definite evidence that hard water is more lithogenic than soft water. Furthermore, water components other than calcium can modify the tendency toward crystal formation, affecting inhibitory power and/or lithogenic salt excretion.