Test Details: 1,25-Dihydroxy vitamin D plays a primary role in the maintenance of calcium homeostasis. A part of circulating 25-hydroxy vitamin D is converted to 1, 25-dihydroxy form in the kidneys. Patients who present with hypercalcemia, hyperphosphatemia and low PTH may suffer from unregulated conversion of vitamin D from mono-hydroxy to dihydroxy form as is seen in granulomatous diseases like Sarcoidosis and nutritionally induced Hypervitaminosis D.