Vitamin D is converted in the liver to 25(OH)D, which is the major circulating metabolite of vitamin D. Serum 25(OH)D concentrations, which reflect both vitamin D intake and endogenous production, should be measured to clinically assess vitamin D status (1). In the kidney, 25(OH)D is converted by 1α-hydroxylase to its active form, 1,25-dihydroxyvitamin D [1,25(OH)2D], which plays a vital role in maintaining bone and muscle health by regulating calcium metabolism. Although 1,25(OH)2D is the active form of vitamin D, its serum level does not correlate with overall vitamin D status and thus is generally not clinically useful (1)