Determinants of Osteopenia in Male Renal-Stone–Disease Patients with Idiopathic Hypercalciuria

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BACKGROUND AND OBJECTIVES: Bone demineralization is frequent in renal-stone formers with hypercalciuria. Although this pathologic link has been recognized for decades, the underlying mechanisms and risk factors associated with osteopenia/osteoporosis in this population remain partially understood. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: This study retrospectively analyzed determinants of low bone mineral density (BMD) in 65 idiopathic hypercalciuric male renal-stone formers. Clinical and biologic evaluation included BMD measurement, bone-remodeling markers, analysis of calcium metabolism with oral calcium load test, and dietary inquiry. RESULTS: Patients with osteopenia (n=23, 35% of the population) presented significantly higher fasting calciuria as compared with normal bone density patients (n=42) (calcium/creatinine ratio was 0.32 versus 0.24 mmol/mmol; P=0.006). Analysis of the whole population revealed a negative association between fasting hypercalciuria and BMD (P = 0.003), independent of confounding variables including body-mass index and tobacco consumption. The fasting calcium/creatinine ratio above 0.25 mmol/mmol was associated with a 3.8-fold increase in the risk of low BMD. CONCLUSION: In our study, fasting hypercalciuria after a 2-day calcium-restricted diet appears as the only biologic factor associated with low BMD, suggesting a bone-calcium efflux. Our results support the view of a parathyroid-independent pathologic process that remains to be identified. Hypercalciuric patients with low BMD do not excrete more calcium in 24-hour urine samples than patients without low BMD.