25(OH) Vitamin D

Vitamin D is a steroid hormone involved in the active intestinal absorption of calcium and in the regulation of its homeostasis. Vitamin D has two isomers: Vitamin D2 and Vitamin D3. Vitamin D2 is obtained from dairy products whereas Vitamin D3 is produced in the skin after exposure to ultraviolet light. In the liver, Vitamin D is hydroxylated at its carbon 25 to form 25-OH Vitamin D. This metabolite is the predominant circulating form of Vitamin D and is considered to be an accurate indicator of the general Vitamin D status of an individual. Vitamin D deficiency has been linked to many diseases including osteoporosis, rickets, osteomalacia, cancers, and cardiovascular diseases. Both dietary supplements of Vitamin D that are currently available in the market (Vitamin D2 and Vitamin D3) are converted to 25-OH Vitamin D in the liver. The sum of the concentrations of 25-OH Vitamin D2 and 25-OH Vitamin D3, in serum or plasma, is referred to as “Total 25-OH Vitamin D”. Accurate monitoring of total 25-OH Vitamin D level is critical in clinical settings. Vitamin D deficient patients who are prescribed a daily Vitamin D supplement should regularly monitor their serum or plasma Vitamin D levels in order to reach an optimal level and prevent their 25-OH Vitamin D concentrations from reaching excessive levels that are considered toxic 1-5.

Catalog number SDL7949
Product type ELISA
Quantity 96 Tests (12×8 breakable strip wells)
Standard range 2.5-150 ng/ml
Analytical Sensitivity 2.5 ng/ml
Sample volume 10 µl/well
Species Human

Application
The SDi 25-hydroxy (25-OH) Vitamin D ELISA is designed for the quantitation of total 25-OH Vitamin D in human serum and plasma.

Principle
The SDi (25-OH) Vitamin D kit is a solid phase enzyme-linked immunoassay (ELISA), based on the principal of competitive binding. anti-Vitamin D antibody coated wells are incubated with Vitamin D standards, controls, samples, and vitamin D-Biotin conjugate at room temperature for 120 minutes. During the incubation, a fixed amount of biotin-labeled vitamin D competes with the endogenous Vitamin D in the sample, standard, or quality control serum for a fixed number of binding sites on the anti Vitamin D antibody. Following a wash step, bound Vitamin D-Biotin is detected with Streptavidin-HRP. Streptavidin-HRP conjugate immunologically bound to the well progressively decreases as the concentration of Vitamin D in the specimen increases. Unbound SA-HRP conjugate is then removed and the wells are washed. Next, a solution of TMB Reagent is added and incubated at room temperature for 30 minutes, resulting in the development of blue color. The color development is stopped with the addition of stop solution, and the absorbance is measured spectrophotometrically at 450 nm. A standard curve is obtained by plotting the concentration of the standard versus the absorbance. The color intensity will be inversely proportional the amount of 25(OH)D in the sample. The assay measures both Vitamin D2 and D3). The total assay procedure run time is 2.5 hours.

Storage and Stability
Product should be stored at 2-8 °C. Product is stable for 24 months from the date of manufacturing.

Precautions
For research use only. Not for use in diagnostic procedures.

References
1. Holick, MF. Vitamin D Status: Measurement, Interpretation and Clinical Application. Ann Epidemoil. 2009, 19(2):73 – 78
2. Morris H. A. Vitamin D: A Hormone for All Seasons-How Much is enough? Clin. Biochem. Rev., 2005, 26, 21-32.
3. Bikle D. D. Vitamin D and the skin. J. Bone Miner. Metab., 2010, 28, 117-30.
4. Zerwekh J. E. Blood biomarkers of vitamin D status. Am. J. Clin. Nutr., 2008, 87, 1087S-91S.
5. Moyad M. A. Vitamin D: a rapid review. Dermatol Nurs., 2009, 21, 25-30.