Vitamin D3 (1,25-OH D3),Serum

This test is done to measure the active form of vitamin D (calcitriol), which plays a key role in calcium and phosphate regulation, bone health, and immune function. Abnormal levels may be seen in kidney disease, parathyroid disorders, or granulomatous diseases such as sarcoidosis. It is not the same as 25-OH vitamin D, which reflects vitamin D stores.