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      Urinary Sodium and Potassium Excretion in Idiopathic Hypercalciuria of Children

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          Background: An increased spot urine Na/K ratio (UNa/K) has been found to be related to urinary stone disease in adults with a history of nephrolithiasis and in children with idiopathic hypercalciuria (HC). However, the respective role played by Na and K excretion in the rise of the UNa/K in growing individuals is not well clarified. Methods: The urinary excretion of Na and K was evaluated in fasting morning and 24-hour urine samples of 37 consecutive children with HC and of 21 previously HC children who were normocalciuric at the time of the study (ExHC). None of them had received any dietary or specific drug prescription. Results: In the HC and in the ExHC group, respectively, the Na excretion was 4 ± (SD) 2.4 and 2.9 ± 1.3 mmol/kg/day (p = 0.009); the K excretion was 1.1 ± 0.4 and 1.2 ± 0.7 mmol/kg/day (p = 0.86); the fasting UNa/K was 3 ± 1.6 and 2.1 ± 1 mmol/mmol (p = 0.044), and the 24-hour UNa/K was 4.2 ± 3.9 and 2.8 ± 1.5 mmol/ mmol (p = 0.045). The 24-hour UNa/K was significantly higher than the fasting UNa/K in both HC (p = 0.002) and ExHC (p = 0.002) subjects. The 24-hour UNa/K significantly increased with age in both HC (p = 0.02) and ExHC (p = 0.015) children. The K excretion significantly decreased with age in HC (p = 0.0001) and ExHC (p = 0.005) subjects, as well as with body weight gain in HC (p = 0.005) and ExHC (p = 0.0001) children and with increasing body height in HC (p = 0.006) and ExHC (p = 0.001) subjects. In neither group was the K excretion significantly related to body mass index Z score nor to height Z score. No significant relation resulted between Na excretion and age, body weight and height, and body mass index Z score and height Z score. Conclusions: HC children have a higher Na excretion as well as a higher fasting and 24-hour UNa/K than ExHC children, but no different K excretion. Meals are accompanied by a significant rise in UNa/K. The rise in UNa/K with age is mostly due to a decrease in K excretion which possibly depends on childhood body growth.

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          The relationship between urinary calcium, sodium, and potassium excretion and the role of potassium in treating idiopathic hypercalciuria.

          1) To evaluate the relationships between urinary sodium (UNa), potassium (UK), and calcium (UCa) excretion in the pediatric population; and 2) to determine the effect of increasing potassium intake in patients with idiopathic hypercalciuria and investigate whether this intervention can be offered as another mode of therapy in this patient population. Prospectively, we determined UNa, UK, UCa, and creatinine (Cr) concentrations in randomly collected urine samples from children on initial evaluation for urinary frequency, dysuria, hematuria, enuresis, or kidney stones to identify children with hypercalciuria. The outpatient renal clinic of an academic hospital. Twenty-three black children (13 girls and 10 boys) and 77 white children (44 girls and 33 boys) 3.92 to 16.67 years of age. Eleven children with hypercalciuria were given potassium supplementation or placed on a high-potassium diet for at least 2 weeks. UNa to UK, UNa to Cr, UK to Cr, and UCa to Cr ratios were calculated from measured levels of urinary minerals. These were repeated in 11 hypercalciuric patients after 2 weeks of increased potassium intake. A total of 100 urine samples were analyzed. The UCa/Cr ratio in blacks 0.04 +/- 0.06 (mean +/- standard deviation) was significantly lower than in whites 0.16 +/- 0.12. There were 21 hypercalciuric white children versus only 1 black child. Linear regression analysis revealed a positive direct correlation between UNa/Cr and UCa/Cr in all 100 subjects and in whites alone but not in blacks. An inverse relationship existed between UK/Cr and UCa/Cr in all subjects and in whites and showed a strong trend in blacks. A marked direct relationship was found between UNa/K and UCa/Cr in all subjects (r = .43) as well as in whites (r = .59) and blacks (r = .49). One black child and 10 white hypercalciuric children were treated with "extra" K for at least 2 weeks. The UNa/K decreased from 4.73 +/- 2.28 to 1.98 +/- 1.09, and the UCa/Cr decreased from 0. 31 +/- 0.10 to 0.14 +/- 0.07, with resolution or improvement of the patients' symptoms. In our patient population with urinary symptoms, the UCa/Cr ratio in black children is lower and hypercalciuria less common than in white children. In both white and black populations, the UNa/K ratio had the strongest association with the UCa/Cr ratio, indicating an opposing role of UNa and UK on the UCa/Cr ratio. Increased potassium intake was found to be beneficial for hypercalciuric children by decreasing the UNa/K ratio and, consequently, the UCa/Cr ratio.
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            Effects of a Meat Meal on Renal Sodium Handling and Sodium Balance


              Author and article information

              S. Karger AG
              May 2002
              02 May 2002
              : 91
              : 1
              : 7-12
              Department of Pediatrics, Second University of Naples, Italy
              57598 Nephron 2002;91:7–12
              © 2002 S. Karger AG, Basel

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              Page count
              Figures: 1, Tables: 3, References: 22, Pages: 6
              Self URI (application/pdf): https://www.karger.com/Article/Pdf/57598
              Pediatric Nephrology. Editor: N.G. De Santo, Naples


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