25-hydroxycholecalciferol is an intermediate metabolite of the vitamin D group that is formed in the liver

• calcidiol (also called 25-hydroxyvitamin D3), is the form measured in the blood to assess vitamin D status
  • in the liver, vitamin D3 is hydroxylated at the 25' position to produce 25-hydroxycholecalciferol (calcidiol). This is then bound to another selective transport protein for transit to the kidneys. Calcidiol is the most abundant form of vitamin D, but is less active than calcitriol

It has a similar structure to calcitriol - which it is metabolised to in the kidneys - but it is relatively less active.