Initial collection of an inadequate 24-hour urine sample in children does not predict subsequent inadequate collections.

INTRODUCTION: Approximately half of adult stone formers submit specimens that are either under or over collections as determined by 24-h creatinine/kg. Previously identified predictors of inadequate collection in adults include female sex, older age, higher body mass index (BMI), vitamin D supplementation, and weekday collection. OBJECTIVE: The objective of this study is to determine risk factors for inadequate 24-h urinary specimen collection in the pediatric population. STUDY DESIGN: A retrospective analysis of all children (<18 years of age) with renal and/or ureteral calculi evaluated at the study tertiary care pediatric center from 2005 to 2015 was performed. Those who had at least one 24-h urinary metabolic profile after a clinical visit for kidney and/or ureteral stones were included; children with bladder stones were excluded. Adequate collections had a urine creatinine of 10-15 mg/kg/24 h. A bivariate analysis of potential factors associated with inadequate collection of the initial urinary metabolic profile, including child demographics, parental socio-economic factors, history of stone surgery, and weekday vs. weekend urine collection, was performed. A mixed-effects logistic regression, controlling for correlation of specimens from the same patient, was also performed to determine whether an initial inadequate collection predicted a subsequent inadequate collection. RESULTS: Of 367 patients, 80 had an adequate collection (21.9%): median age, 13 years (interquartile range, 8-16); 61.1% female; 93.5% white; 19.5% obese; and 13.0% overweight. No parental or child factors were associated with inadequate collection (Summary Table). Of inadequate collections, more than 80% were over collections. In the 175 patients with more than one 24-h urinary specimen collection, the effect of an initial inadequate collection on subsequent inadequate collections was not significant after controlling for the correlation of samples from the same patient (p = 0.8). DISCUSSION: Any parental or child factors associated with the collection of inadequate 24-h urine specimens in children were not found. An initial inadequate collection does not predict subsequent inadequate collections. It was surprising that >80% of the inadequate collections were over collections rather than under collections. Possible explanations are that children collected urine samples for longer than the 24-h period or that stone-forming children produce more creatinine per 24-h period than healthy children due to hyperfiltration. CONCLUSION: Inadequate collections are very common, and the risk factors for them are unclear. A repeat collection would be suggested if the first is inadequate. Further studies must be planned to explore barriers to accurate specimen collection using qualitative research methodology.

Higher urinary potassium is associated with decreased stone growth after shock wave lithotripsy.

PURPOSE: We correlated serum and urinary biochemical parameters with radiological evidence of stone growth after shock wave lithotripsy. MATERIALS AND METHODS: Biochemical parameters in serum and 24-hour urine collections of 359 patients were correlated with stone growth for 2 years after shock wave lithotripsy. Each patient underwent a minimum of 2 radiological studies at 3 and 12 months and plain abdominal x-ray at 24 months. The presence and size of stones were documented by a radiologist in blinded fashion. Stone growth was defined as measurable growth of a preexisting stone or new stone formation. RESULTS: A total of 209 patients remained stone-free or had no existing stone growth, while stone size decreased in 30. Of the remaining 120 patients with stone growth 72 had new growth and 48 had growth of preexisting stones. Urinary excretion of potassium was significantly higher in those without than with stone growth (mean 24-hour urine collection plus or minus standard deviation 62 +/- 27 versus 54 +/- 23 mmol., p = 0.009). The only parameter significantly associated with stone growth was urinary potassium. Linear regression revealed that for each 10 unit increase in urinary potassium there was a corresponding 2 mm. decrease in stone growth (p = 0.013). CONCLUSIONS: Our results indicate that increased urinary potassium excretion correlates with a decreased risk of stone growth up to 2 years after shock wave lithotripsy, implying that a high potassium diet may be beneficial for preventing stone growth. The effect of potassium supplementation on stone formation and growth must be investigated further.

Urinary biochemical profile of patients with ureteric calculi in Jodhpur region (north western India).

Urine chemistry of 42 normal subjects (NS) and 59 ureteric stone formers (SF) from Jodhpur region of Rajasthan, India is presented. Twenty four hour urinary levels of calcium, oxalic acid and uromucoids were significantly higher and levels of magnesium, citric acid and inorganic phosphorus were significantly lower in SF as compared to NS. No significant difference was observed in the uric acid, sodium and potassium levels in the two groups. Significant correlation was observed between calcium and magnesium; calcium and oxalic acid; calcium and citric acid; magnesium and oxalic acid; and oxalic acid and citric acid in NS on the basis of mmol/l but not on the basis of mmol/24 h. Calcium and oxalic acid correlation was uninfluenced by magnesium and citric acid levels. The log of risk factor index (RI) was higher (p less than 0.001) in SF (-1.652) as compared to NS (-2.103). The log of ion activity product (IAP) was also higher (p less than 0.001) in SF (-3.192 X 10(-3)) than in NS (-2.914 X 10(-1)). Based on RI and IAP, a scale has been devised for the prediction of the risk of stone formation and recurrence.

Influence of indwelling urinary tract stones on twenty-four-hour urine chemistries.

Twenty-two patients with ureteral stones underwent twenty-four-hour urinary excretion studies of calcium, phosphorus, and uric acid before and after stone elimination from the urinary tract. Comparison of pre- and post-stone elimination studies showed no significant differences suggesting that the presence of stones in the urinary tract has little influence on the twenty-four-hour urinary excretion of calcium, phosphorus, and uric acid.