Which form of vitamin D is typically used for screening?

The correct choice for screening vitamin D levels is 25-hydroxy vitamin D. This form of vitamin D is the primary circulating metabolite in the blood and serves as the best indicator of overall vitamin D status in the body.

When evaluating a person's vitamin D levels, measuring 25-hydroxy vitamin D provides insight into both dietary intake and sunlight exposure. It reflects the total amount of vitamin D—both from food (vitamin D2 and D3) and from skin synthesis—in the body, making it a reliable marker for assessing deficiency or sufficiency.

The other forms of vitamin D mentioned do not serve as useful measures for screening. (1,25) dihydroxy-vitamin D is the active form of the vitamin and generally does not reflect stores accurately because it has a much shorter half-life and is tightly regulated by the parathyroid hormone and calcium levels. Making it a poor choice for gauging vitamin D status in the general population. While vitamin D3 and D2 are worth noting as sources of vitamin D, they do not directly measure the levels of the metabolite indicative of the body’s stores of vitamin D, which is what screening aims to determine.