Patent ID: 8431411

Claim:
A method for diagnosing vitamin D deficiency in a patient comprising: (a) generating a protonated and dehydrated precursor ion of a vitamin D metabolite obtained from a patient sample, wherein said vitamin D metabolite is 25-hydroxyvitamin D 3 or 25-hydroxyvitamin D 2 , and said protonated and dehydrated precursor ion of 25-hydroxyvitamin D 3 has a mass to charge ratio (m/z) of 383.16±0.5, and said protonated and dehydrated precursor ion of 25-hydroxyvitamin D 2 with an m/z of 395.30±0.5; (b) generating one or more fragment ions of said precursor ion; (c) detecting the amount of one or more of said ions generated in step (a) or (b) or both and relating the amount of detected ions to the amount of 25-hydroxyvitamin D 3 or 25-hydroxyvitamin D 2 in said sample; and (d) diagnosing a patient as having a vitamin D deficiency when the amount of said 25-hydroxyvitamin D 3 or 25-hydroxyvitamin D 2 in said sample is reduced relative to the amount of said 25-hydroxyvitamin D 3 or 25-hydroxyvitamin D 2 in individuals without a vitamin D deficiency; wherein the generating and detecting steps are carried out using tandem mass spectrometry.