Renal and absorptive hypercalciuria: A metabolic disturbance with varying and interchanging modes of expression

Background. In previous studies, the oral calcium loading and deprivation test has been used to distinguish between children with renal (fasting) hypercalciuria (RH) and absorptive hypercalciuria (AH). Objective. We evaluated the long-term clinical course of 30 children with idiopathic hypercalciuria and investigated the influence of urinary sodium excretion, as a reflection of its intake, on urinary calcium excretion. Methods. Thirty normocalcemic, normophosphatemic children (21 boys and 9 girls) with urinary calcium to creatinine ratios greater than 0.57 mmol/L/mmol/L (>0.21 mg/dL/mg/dL) on three consecutive examinations participated in this study. They were divided according to their responses to calcium deprivation and loading into AH (16 patients) and RH (14 patients). Results. When restudied 3 to 7 years later, 6 of the 16 children with AH were normocalciuric and three demonstrated characteristics compatible with RH. The remaining seven patients maintained their initial AH pattern. Of the 14 children with RH, four were normocalciuric and four demonstrated AH. The remaining six children maintained their initial RH pattern. A significant positive correlation was observed between urine sodium and calcium excretion in children with AH or RH. Children who were normocalciuric at the second study had significantly lower values of urine sodium excretion when compared with those in whom hypercalciuria persisted. Conclusions. We suggest that AH and RH constitute a continuum. The change in characteristics observed during the second study suggests that any attempt to divide these patients into two physiologically distinct-subtypes may be artificial. The main factor influencing urinary excretion of calcium in our patients seemed to be sodium intake.