Vitamin D – 25 OH


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The DRG:HYBRiD-XL 25-OH Vitamin D (total) is an enzyme immunoassay for the quantitative in vitro diagnostic measurement of 25_OHVitaminD in serum and plasma.
Only for use with the DRG:HYBRiD-XL Analyzer.

VitaminD is a steroid hormone involved in the intestinal absorption of calcium and the regulation of calcium homeostasis. The two major forms of VitaminD, named Vitamin D3 (cholecalciferol) and Vitamin D2 (ergocalciferol), have isomeric structures, but D2 is supposed to be less active than D3 1. Physiological VitaminD3 levels result not only from
dietary uptake but can also be produced from a cholesterol precursor, 7-dehydro_cholesterol, in the skin during sun exposure. D2 is obtained from plant sources and only represents less than 5% of the total VitaminD in the body2. In the liver, the VitaminD is hydroxylated to 25-hydroxyvitaminD (25-OH D), the major circulating metabolite of VitaminD. VitaminD and 25-OH D enter the circulation bound to VitaminD 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 di_hydroxy_vitaminD (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 VitaminD, it is widely accepted that the measurement of circulating 25_OHD provides better information with respect to patients VitaminD 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 VitaminD deficiency in different European countries is critically discussed 6. VitaminD intoxication mostly occurs during a large intake of pharmaceutical preparations of VitaminD 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_OHVitaminD of a patient sample competes with a 25_OHVitaminD-biotin (Enzyme
Conjugate) for binding to the coated VDBP. After incubation the unbound conjugate is washed off. Thereafter, bound 25-OH Vitamin D-biotin conjugate is detected by
streptavidin-conjugated peroxidase (Enzyme Complex). The amount of bound peroxidase conjugate is inversely proportional to the concentration of 25_OHVitaminD in the sample. Having added the substrate solution, the intensity of colour developed is inversely proportional to the concentration of 25_OHVitaminD in the patient sample.

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