Metabolic Evaluation: Place of the Calcium Load Test: How, When, For Whom, and Why?

Most human urinary stones are calcium-based and are often associated with hypercalciuria. A simple test described in 1975 by Pak et al allows for pathogenic classification of hypercalciuria: the calcium load test (CLT). The CLT explores calcium homeostasis after a low-calcium diet and then a calcium load (typically oral administration of 1 g of elemental calcium). Only simple laboratory equipment is required. Inadequate calcium excretion after a calcium-free diet or a calcium load is suggestive of resorptive or absorptive hypercalciuria, respectively. The CLT is particularly valuable in diagnosing primary hyperparathyroidism, even in most early stages of this disease. PATIENT SUMMARY: Kidney stone formation can be linked to calcium metabolism. When high calcium levels are found in urine despite adequate diet changes, a calcium load test may help to understand the underlying mechanisms. Urine and blood levels are explored during a low-calcium diet phase, and after a calcium load phase in the test. The calcium load test is particularly advantageous for revealing abnormally high function of the parathyroid gland, which is called hyperparathyroidism.