Measurement of vitamin D.

There are many different methods to choose for vitamin D analysis. While immunoassays are available commercially and readily automated, specificity for 25-hydroxyvitamin D2 and D3 is variable. Chemical assays such as HPLC and LC-MS/MS have greater specificity and are capable of detecting 25-hydroxyvitamin D2 and D3 separately, but are more complex and require method development. Currently LC-MS/MS is considered the method of choice for 25-hydroxyvitamin D analysis and the methods given here are for LC-MS/MS analysis of serum, plasma and dried whole blood for the separate quantitation of 25-hydroxyvitamin D2 and D3. In addition to highlighting potential interferences, the many non-analytical factors that influence vitamin D measurement are also discussed.