<prompt> Form of vitamim D which is measured in serum ?Cholecalciferol25 hydroxyvitamin D1,25 dihydroxyvitamin D24,25 dihydroxyvitamin D  <response>: Ans. is b i.e., 25 hydroxyvitamin DThough, 1, 25 dihydroxyvitamin D calcitriol is the active form of vitamin D, its serum measurement does not provide any information about vitamin D status because it is often normal or elevated due to secondary hyperparathyroidism associated with vitamin D deficiency...Measurement of 25 hydroxyvitamin D calcifedial in serum provides more accurate information of vitamin D status. The usual values are :- 20 ngml - Deficiency20-29 ngml - Insufficiency30-100 ngml - Normal 100 ngml - Toxicity 