Study of calcium metabolism in idiopathic hypercalciuria by strontium oralload test

Calcium excretion and absorption were evaluated in hypercalciuric calcium s tone formers by the study of Sr2+ excretion and absorption after an oral lo ad. Ca2+ stone formers (n = 140) were studied, and the results were compare d in the 83 of them who had idiopathic hypercalciuria and in the 57 who had Ca2+ excretion within reference values. Hypercalciuric patients showed inc reased renal Sr2+ clearance (CRE; 5.26 +/- 0.358 vs 3.29 +/- 0.277 mL/min; P <0.001), whereas Sr2+ absorption [assessed as the area under the serum co ncentration-time curve (AUC)] was increased at 30 and 60 min (1.53 +/- 0.08 7 vs 1.21 +/- 0.071 mmol.L-1.min; P <0.05), but not at 240 min after the lo ad. In hypercalciuric patients, the AUCs were positively correlated with ur inary Sr2+ fractional excretion (P <0.001). Conversely, in normocalciuric p atients plasma parathyroid hormone (PTH) was negatively correlated with the AUCs (P <0.01) and CRE (P <0.05), whereas 1,25-dihydroxyvitamin D plasma c oncentrations normalized to PTH were positively correlated with the AUCs (P <0.05). The results of Sr2+ load tests suggest that in the hypercalciuric population, Ca2+ absorption is altered predominantly in the duodenum and th at the normal regulation exerted by calciotropic hormones on tubular and en teral Ca2+ handling is lost.