1 Other disadvantages to current methods include use of radioactive isotopes, method-to-method variation, and laboratory-to-laboratory variation. Additionally, some analytical methods may underestimate 25OHD concentration when significant amounts of 25OHD2 are present owing to diminished cross-reactivity. Most current methods do not differentiate between the 2 forms: only total 25OHD concentrations are reported. Thus, analytical methods that can accurately quantitate both 25OHD forms are essential for diagnosis and monitoring patients with vitamin D disorders. Furthermore, both forms are metabolized to their respective 25OHD forms (i.e., 25OHD3 and 25OHD2).
Both forms of the vitamin are used to fortify various foods and in over-the-counter supplements, and vitamin D2 is used in a high potency (50,000 IU) formulation for treating severe vitamin D deficiency. Vitamin D3 is obtained from foods of animal origin and from ultraviolet light-stimulated conversion of 7-dehydrocholesterol in the skin, whereas small amounts of vitamin D2 are obtained from foods of plant origin. Vitamin D occurs in 2 forms: vitamin D3 (cholecalciferol) and vitamin D2 (ergocalciferol). Because of its long half-life, 25OHD measurements are useful for assessing vitamin D status in patients. Monitor therapeutic response in patients being treated for vitamin D-related disordersĢ5-Hydroxyvitamin D (25OHD) is the major circulating form of vitamin D and the precursor of the active form (1, 25-dihydroxyvitamin D).
Diagnose intestinal malabsorption and vitamin D deficiency or intoxication
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