Vitamin D, 1,25-OH (Calcitriol)

What it isCalcitriol is the active hormonal form of vitamin D, produced by the kidneys from 25-OH vitamin D. It binds the vitamin D receptor and drives gene expression.

DoesRegulates calcium absorption from the gut, modulates immune, and influences hundreds of genes.

GoodA mid-range calcitriol with appropriate 25-OH vitamin D signals balanced vitamin D physiology.

BadCalcitriol can be normal or high even when 25-OH vitamin D is low — making it a poor screening test. It rises pathologically in granulomatous disease (sarcoidosis, tuberculosis) and some lymphomas.