1,25-dihydroxy vitamin D (1,25DHD) is the active form of vitamin D, produced primarily by the kidney by hydroxylation of 25-hydroxy vitamin D. 1,25DHD is the form of vitamin D that stimulates resorption of calcium from bone, intestinal absorption and renal reabsorption.

NB. 1,25DHD should not be used to determine vitamin D status; 25-hydroxy vitamin D is the best marker for this purpose.

Indications for 1,25DHD are limited. Measurement may be useful in the investigation of possible vitamin D-dependent rickets and in patients with hypercalcaemia to investigate possible excess 1,25DHD production e.g. granulomatous diseases (sarcoidosis, TB or lymphoma). 

Sample Requirements and Reference Ranges