A case of hypercalcemia Indications for 1,25-dihydroxyvitamin D prescription

Circulating vitamin D is found in various forms: 25-hydroxyvitamin D or calcidiol, majority circulating form, is a "pro-hormon" which will be converted to 1,25-dihydroxyvitamin D or calcitriol, hormone corresponding to vitamin D active form. While determination of 25-hydroxyvitamin D serum levels reflects vitamin D status of patients, determination of 1,25-dihydroxyvitamin D serum level is only indicated in rare cases of suspected hypersensitivity vitamin D in children or of sarcoidosis in adults. There are too many confusion between these two vitamin forms, resulting in inappropriate prescription of 1,25-dihydroxyvitamin D. Here, we describe a case of hypersensitivity to vitamin D by mutation of CYP24A1. We propose to review the interest of 1,25-dihydroxyvitamin D assay in different pathologies, to describe the assay techniques and remind the good prescribing practices of this parameter.