Assessment of the calcium loading test in differentiating between various forms of idiopathic hypercalciuria

The oral calcium loading test for the differential diagnosis of the various forms of idiopathic hypercalciuria has raised much interest, since it might provide the basis for a selective, optimal treatment of the different hypercalciuric states. We have assessed the ability of this test to differentiate between the two major forms of idiopathic hypercalciuria: renal and absorptive hypercalciuria. The test was performed in 32 idiopathic hypercalciuria patients. Based on generally accepted criteria that have been established according to the results of calcium and cAMP measurements in plasma and urine, 31% of the patients could be classified as having renal hypercalciuria and 13% as having absorptive hypercalciuria, whereas the remaining 56% did not fit either of these categories. In view of the expense and logistics involved in performing the test, the finding of an approximately 50% efficacy rate in distinguishing between the forms of idiopathic hypercalciuria raises serious doubts regarding the value of its routine implementation.