Phosphate homeostasis in Bartter syndrome: a case-control study.

Background: Bartter patients may be hypercalciuric. Additional abnormalities in the metabolism of calcium, phosphate, and calciotropic hormones have occasionally been reported. Methods: The metabolism of calcium, phosphate, and calciotropic hormones was investigated in 15 patients with Bartter syndrome and 15 healthy subjects. Results: Compared to the controls, Bartter patients had significantly reduced plasma phosphate {mean [interquartile range]:1.29 [1.16-1.46] vs. 1.61 [1.54-1.67] mmol/L} and maximal tubular phosphate reabsorption (1.16 [1.00-1.35] vs. 1.41 [1.37-1.47] mmol/L) and significantly increased parathyroid hormone (PTH) level (6.1 [4.5-7.7] vs. 2.8 [2.2-4.4] pmol/L). However, patients and controls did not differ in blood calcium, 25-hydroxyvitamin D, alkaline phosphatase, and osteocalcin levels. In patients, an inverse correlation ( P < 0.05) was noted between total plasma calcium or glomerular filtration rate and PTH concentration. A positive correlation was also noted between PTH and osteocalcin concentrations ( P < 0.005), as well as between chloriduria or natriuria and phosphaturia ( P < 0.001). No correlation was noted between calciuria and PTH concentration or between urinary or circulating phosphate and PTH. Conclusions: The results of this study demonstrate a tendency towards renal phosphate wasting and elevated circulating PTH levels in Bartter patients. [ABSTRACT FROM AUTHOR]