25-OH-vitamin D (25OHD) is ordered and interpreted clinically in light of calcium balance and homeostasis. Various methodologies including immunoassay and chromatography are described for the measurement of 25OHD in biological fluids. It is well reported that all existing methods are challenging and require a high level of technical expertise. While this is also true of the methods using liquid chromatography-tandem mass spectrometry (LC-MS-MS), the technique is gaining favor in various laboratories because it offers advantages of greatly improved specificity and sensitivity.
