Introduction 25-hydroxyvitamin D (25-OH vitamin D) is the main circulating metabolite of vitamin D (1). While the biological active form of vitamin D is 1,25(OH)2 vitamin D, synthesized in the kidney, it is broadly accepted that the measurement of circulating 25(OH) vitamin D offers better evidence with respect to the patients’ vitamin D status (1,2). Recently, various studies have shown the ro...