High circulating levels of 25-hydroxyvitamin D₃in renal stone formers with hyperabsorptive hypercalciuria

Abstract

Normocalcaemic male stone formers, 31-51 years old (n=108) on a free diet, were divided into a hypercalciuric group (n=47) with calcium excretion rates higher than 8.0 mmol/24 h, a normocalciuric group (n=32) with calcium excretion rates below 6.1 mmol/24 h and an intermediate group (n=29). There were no statistically significant differences between the hypercalciuric and the normocalciuric groups with respect to serum levels of calcium, phosphate, creatinine, urate, ALAT, albumin, PTH, 1,25-dihydroxyvitamin D or urinary excretion of cAMP. The group of patients with high calcium excretion had significantly higher serum levels of 25-hydroxyvitamin D3 (75 ±4 nmol/1) than the group with low calcium excretion (57±4 nmol/1) (p<0.002), while the group of patients with intermediate calcium excretion had 25-hydroxyvitamin D3 levels between the other two groups (69±4 nmol/1). A highly accurate method based on isotope dilution mass spectrometry was used to assay 25-hydroxyvitamin D3. Of the patients with hypercalciuria (n=47), seven were classified as hyperabsorbers on the basis of calcium load tests. These patients were found to have even higher serum levels of 25-hydroxyvitamin D3 (108±10 nmol/1) significantly higher than that of the hypercalciuric patients as a whole. The above study was carried out in March 1983. In September, the group of patients with high urinary calcium excretion also had significantly higher levels of 25-hydroxyvitamin D3 than the group of patients with low calcium excretion. The possibility that increased serum levels of 25-hydroxyvitamin D3 may be of some importance in the development of hypercalciuria is discussed.