Testing for 1-25 dihydroxy Vitamin D

Assessing nutritional vitamin D status requires measuring 25-hydroxyvitamin D, as serum 1,25-dihydroxyvitamin D is tightly regulated by parathyroid hormone, calcium, and phosphate, often remaining normal or paradoxically elevated in severe nutritional deficiency due to secondary hyperparathyroidism. Clinical ordering of 1,25-dihydroxyvitamin D must be strictly reserved for evaluating complex disorders of calcium homeostasis, granulomatous diseases, lymphomas, advanced chronic kidney disease, or rare hereditary rickets. Inappropriate ordering misleads clinical management, triggers insurance reimbursement denials, and increases low-value healthcare expenditure. Clinicians should treat 1,25-dihydroxyvitamin D exclusively as a specialized endocrine regulator rather than a screening tool for vitamin D stores.