https://www.medscape.com/viewarticle/937756
The total amount of these vitamin D metabolites is most often used to assess a patient's vitamin D status; 25(OH)D is the prohormone that is converted to 1.25(OH)2D. The latter is considered the "active" form of vitamin D in the body.
Men with the lowest free 25(OH)D levels (<4.43 ng/L) had a 91% increased risk for all-cause mortality compared to those with the very highest amount of free 25(OH)D, reported Antonio.