SENSITIVITY TO CALCIUM INTAKE IN CALCIUM STONE FORMING PATIENTS

The absorptive or renal origin of hypercalciuria can be discriminated using an acute oral calcium load test (ACLT). Of 86 patients with calc ium oxalate kidney stones, 28 (23%) were found to be hypercalciuric (H Ca) and 58 (67%) normocalciuric (NCa) on their customary free diet, co ntaining 542 +/- 29 mg/day (mean +/- SE) of calcium. Since the apparen tly normal 24-hour calcium excretion of many calcium stone formers (CS F) may be due to a combination of high calcium absorption with moderat ely low calcium intake, all patients were investigated by ACLT. Of 28 HCa patients, 13 (46%) were classified as absorptive (AH) and 15 (54%) as renal hypercalciuria (RH). Of the 58 NCa patients, 38 (65%) presen ted features of intestinal hyperabsorption and were therefore designat ed as AH-like, and 20 (35%) as RH-like. To further elucidate the role of dietary calcium in these CSF, a chronic calcium load test (CCLT), c onsisting of 1 g/day of oral Ca for 7 days, was designed. A positive r esponse to the CCLT was considered to occur when urinary calcium (uCa) was greater than or equal to 4 mg/kg/24 h on the 7th day. Among NCa p atients, 29% of AH-like subjects responded to the CCLT and 71% did not ; 50% of RH-like subjects also responded and 50% did not. In HCa patie nts, 85% of AH and 67% of RH subjects maintained uCa greater than or e qual to 4 mg/kg/24 h after the CCLT and 15% of AH and 23% of RH subjec ts did not. However, a significant additional increase in mean uCa was not observed among HCa patients. All patients were submitted to a sec ond evaluation of fasting calciuria (Ca/Cr). A modification of this pa rameter was noticed in 89% of RH-like and 78% of RH patients, In concl usion, these data suggest the presence of subpopulations of patients s ensitive or not to calcium intake, regardless of whether the acute res ponse to a calcium overload test suggested AH or RH. The CCLT disclose d dietary hypercalciuria in 21/58 (36%) of previously NCa patients. In these NCa patients, the ACLT may be replaced by the CCLT. The distinc tion between AH and RH initially evidenced by the ACLT was not further confirmed. These data suggest that either fasting Ca/Cr is not adequa te for subclassification of HCa or that AH and RH represent a differen t spectrum of the same disease, and that a primary resorptive componen t should also be considered.