Vitamin D - 25 OH

The DRG:HYBRiD-XL 25-OH Vitamin D (total) is an enzyme immunoassay for the quantitative in vitro diagnostic measurement of 25-OH Vitamin D in serum and plasma.Only for use with the DRG:HYBRiD-XL Analyzer.Vitamin D is a steroid hormone involved in the intestinal absorption of calcium and the regulation of calcium homeostasis. The two major forms of Vitamin D, named Vitamin D3 (cholecalciferol) and Vitamin D2 (ergocalciferol), have isomeric structures, but D2 is supposed to be less active than D3 1. Physiological Vitamin D3 levels result not only fromdietary uptake but can also be produced from a cholesterol precursor, 7-dehydro­cholesterol, in the skin during sun exposure. D2 is obtained from plant sources and only represents less than 5% of the total Vitamin D in the body2. In the liver, the Vitamin D is hydroxylated to 25-hydroxyvitamin D (25-OH D), the major circulating metabolite of Vitamin D. Vitamin D and 25-OH D enter the circulation bound to Vitamin D binding protein (VDBP). Upon request, a small portion of 25-OH D is further hydroxylated in the kidney to form the biologically active hormone 1,25 di­hydroxy­vitamin D (1,25-(OH)2 D) 3. This process is tightly regulated by the concentration of 1,25-(OH)2 D, parathyroid hormone,hypophosphatemia and ionized calcium levels. Concentrations of 1,25-(OH)2 are about 1000-fold lower than that of 25-OH D 4. Although 1,25-(OH)2 D portrays the biological active form of Vitamin D, it is widely accepted that the measurement of circulating 25-OH D provides better information with respect to patients Vitamin D status and allows its use in diagnosis of hypovitaminosis 5. The concentration of 25-OH D decreases during winter time (reduced sun exposure), with dark skin colour and with age 6. Determination of 25-OH D in serum or plasma will support the diagnosis and therapy control of postmenopausal osteoporosis, rickets in children, osteomalacia, renal osteodystrophy, neonatal hypocalcemia and hyperparathyroidism. In addition, the effects of prevailing subclinical Vitamin D deficiency in different European countries is critically discussed 6. Vitamin D intoxication mostly occurs during a large intake of pharmaceutical preparations of Vitamin D and may lead to hypercalcemia and nephrocalcinosis in susceptible infants.The DRG:HYBRiD-XL 25-OH Vitamin D (total) Kit is a solid phase enzyme-linked immunosorbent assay (ELISA) based on the principle of competitive binding. The wells (ACW) of the reagent cartridges are coated with Vitamin D Binding Protein (VDBP). Endogenous 25-OH Vitamin D of a patient sample competes with a 25-OH Vitamin D-biotin (EnzymeConjugate) for binding to the coated VDBP. After incubation the unbound conjugate is washed off. Thereafter, bound 25-OH Vitamin D-biotin conjugate is detected bystreptavidin-conjugated peroxidase (Enzyme Complex). The amount of bound peroxidase conjugate is inversely proportional to the concentration of 25-OH Vitamin D in the sample. Having added the substrate solution, the intensity of colour developed is inversely proportional to the concentration of 25-OH Vitamin D in the patient sample.