Oral calcium load test for recurrent calcium stone-formers

Background
Calcium is the most frequent component of urinary stones, and hypercalciuria is the main risk factor in recurrent stone-formers. The oral calcium load test is a dynamical biological test that determines the origin of hypercalciuria in order to optimize the treatment. However, there is little literature about it, and it seems to have lost popularity in daily practice, this why we studied a population of stone-formers who underwent the oral calcium load test.
Methods
Between 2013 and 2016, we prospectively recruited 117 recurrent calcium stone-formers. After 2 days of calcium restricted-diet, patients had urinary and blood sampling at baseline and 120 min after the intake of 1 g of calcium per os. Blood and urinary parameters were assessed during the dynamical test, including stone risk factors, calcium metabolism and bone evaluation. According to these results, patients were classified in three groups: resorptive, renal or absorptive hypercalciuria.
Results
First, 19 patients were diagnosed with normocalcemic primary hyperparathyroidism, assessed by inappropriate parathormone decrease (41.41±12.82 vs. 54.06±13.84% p<0.01) in regard to calcemia. The measurement of ionized calcium was mandatory in order to detect induced hypercalcemia after calcium intake. These patients also had higher beta-crosslaps, lower phosphate reabsorption threshold and lower distal third radius bone mineral density. The treatment of this first group of patient is the hyperparathyroïdectomy. Fasting hypercalciuria was present in 39 patients with urinary calcium >0.37mmol/mmol of creatinine, and without hyperparathyroidism, classified thus as renal hypercalciuria. The treatment of these patients should include adapted calcium intake and thiazids. The third group included 34 patients with absorptive hypercalciuria defined by the presence of delta urinary calcium/creatinine <0.6mmol/mmol between 0 and 120 min, and without any other significant abnormality. Finally, the test result was not reliable for 33 cases because of the absence of sufficient calcemia increase or when the cause of lithogenesis could not be clearly identified.
Conclusions
The oral calcium load test was successful for the identification of main metabolic conditions leading to urolithiasis, including normocalcemic primary hyperparathyroidism, and is useful to improve and personalize the treatment of stone-formers.