Limitations of the oral calcium loading test in the management of the recurrent calcareous renal stone former.

Twenty-two patients with idiopathic hypercalciuria were evaluated using an oral calcium loading test and compared with 20 normal controls. Following a 12-hour overnight fast, all subjects collected a two-hour urine sample after which they received 1 g elemental calcium as galacto-gluconate in milk. Two further two-hour urine collections were obtained consecutively following the oral calcium load. In the fasting state, 4 (18%) of the 22 patients had urinary calcium excretion (UCaE) above normal, but none had elevated iPTH or urinary cAMP values. After calcium loading, only 10 (45%) of the 22 patients had delta UCaE greater than controls (delta = difference in UCaE between third and first urine samples). We conclude that despite demonstrable differences between the mean values of patient and control groups with respect to the UCaE following calcium loading, the large overlap of values negates the clinical usefulness of such procedures in the routine management of individual patients. The definition of renal leak hypercalciuria based on a high fasting UCaE alone remains of uncertain significance.