The potential benefits of maintaining sufficient vitamin D levels has led to a steady increase in testing of vitamin D status in the general population.  This increase has impacted laboratories in a variety of ways, as organizations adapt to growing demand while striving for accuracy and test standardization.The potential benefits of maintaining sufficient vitamin D levels has led to a steady increase in testing of vitamin D status in the general population.  This increase has impacted laboratories in a variety of ways, as organizations adapt to growing demand while striving for accuracy and test standardization. “The (Sun)Light and Dark of 25-Hydroxyvitamin D Testing” was published in the November 2018 issue of the Journal of Applied Laboratory Medicine.  The Review details some of the analytical issues surrounding vitamin D in laboratory testing.