THE RELATIONSHIP BETWEEN URINARY CALCIUM, SODIUM, AND POTASSIUM EXCRETION AND THE ROLE OF POTASSIUM IN TREATING IDIOPATHIC HYPERCALCIURIA

Objectives. 1) To evaluate the relationships between urinary sodium (U Na), potassium (UK), and calcium (UCa) excretion in the pediatric popu lation; and 2) to determine the effect of increasing potassium intake in patients with idiopathic hypercalciuria and investigate whether thi s intervention can be offered as another mode of therapy in this patie nt population. Design. Prospectively, we determined UNa, UK, UCa, and creatinine (Cr) concentrations in randomly collected urine samples fro m children on initial evaluation for urinary frequency, dysuria, hemat uria, enuresis, or kidney stones to identify children with hypercalciu ria. Setting. The outpatient renal clinic of an academic hospital. Par ticipants. Twenty-three black children (13 girls and 10 boys) and 77 w hite children (44 girls and 33 boys) 3.92 to 16.67 years of age. Inter ventions. Eleven children with hypercalciuria were given potassium sup plementation or placed on a high-potassium diet for at least 2 weeks. Outcome Measures. 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 pota ssium intake. Results. A total of 100 urine samples were analyzed. The UCa/Cr ratio in blacks 0.04 +/- 0.06 (mean +/- standard deviation) wa s significantly lower than in whites 0.16 +/- 0.12. There were 21 hype rcalciuric white children versus only 1 black child. Linear regression analysis revealed a positive direct correlation between UNa/Cr and UC a/Cr in all 100 subjects and in whites alone but not in blacks. An inv erse relationship existed between UK/Cr and UCa/Cr in all subjects and in whites and showed a strong trend in blacks. A marked direct relati onship was found between UNa/K and UCa/Cr in all subjects (r(2) = .43) as well as in whites (r(2) = .59) and blacks (r(2) = .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 1.9 8 +/- 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. Conclusi ons, In our patient population with urinary symptoms, the UCa/Cr ratio in black children is lower and hypercalciuria less common than in whi te children. In both white and black populations, the UNa/K ratio had the strongest association with the UCa/Cr ratio, indicating an opposin g role of UNa and UK on the UCa/Cr ratio. Increased potassium intake w as found to be beneficial for hypercalciuric children by decreasing th e UNa/K ratio and, consequently, the UCa/Cr ratio.