1,25-Dihydroxycholecalciferol (Dihydroxyvitamin D, LAB536)

Vitamin D is an essential vitamin that is used for calcium regulation and normal bone development. Concentration of vitamin D is most often assessed in the workup of vitamin D deficiency, which is associated with low serum concentrations of calcium and hyperparathyroidism. The 25-hydroxyvitamin D test is the preferred initial test for assessing vitamin D status and most accurately reflects the body’s vitamin D stores.

1,25 dihydroxyvitamin D is the active metabolite of 25-hydroxyvitamin D. It is a send-out test and should only be ordered rarely. It is appropriate to order in the following scenarios:

• In hypercalcemic patients with low PTH and vitamin D <100 ng/mL,
• In patients with known sarcoidosis/granulomatous disease for whom 25-hydroxyvitamin D supplementation is being assessed,
• To diagnose rare CYP27B1 enzyme disorders or vitamin D mutations in pediatric patients.

• 1,25 dihydroxyvitamin D can be low in patients with renal failure, but measurement is not recommended by KDIGO, as it does not change patient management.

• Without a known history of sarcoidosis, 1,25 dihydroxyvitamin D should primarily be ordered in hypercalcemic patients with low PTH and vitamin D <100 ng/mL.

1. LeFevre ML, on behalf of the USPSTF. Screening for vitamin D deficiency in adults: US Preventive Services Task Force recommendation statement. Annals of Internal Medicine 2015;162:133-140.