Vitamin D, 25-OH, Total Level

Vitamin D is a fat-soluble hormone essential for the regulation of calcium and phosphorus homeostasis and the maintenance of bone health. Increasing evidence also supports a role for vitamin D in cardiovascular disease, cancer, and autoimmune disorders.

Vitamin D is obtained through cutaneous synthesis following sun exposure (vitamin D₃), dietary intake (vitamin D₂ or D₃), and supplementation. It is metabolized in the liver to 25-hydroxyvitamin D [25-OH vitamin D], the major circulating form and precursor to the biologically active metabolite, 1,25-dihydroxyvitamin D. Due to its stability and relatively long half-life of approximately three weeks, serum 25-OH vitamin D measurement is the preferred indicator of vitamin D status.

The Vitamin D, 25-OH, Total assay measures both 25-OH vitamin D₂ and 25-OH vitamin D₃ equally. This competitive immunoassay is performed using the VITROS 25-OH Vitamin D Total Reagent Pack on the VITROS ECi Immunodiagnostic System. Vitamin D, 25-OH in the patient sample competes with horseradish peroxidase (HRP)–labeled vitamin D for binding to monoclonal anti-vitamin D antibodies. The emitted chemiluminescent signal is inversely proportional to the concentration of vitamin D, 25-OH present in the sample.

Store/transport at 15–30°C for ≤72 hours; 2–8°C for ≤7 days; freeze at ≤ –20°C if delayed (stable up to 1 year frozen). Avoid repeated freeze–thaw cycles.

Hemolyzed or lipemic specimens.

Enhanced chemiluminescence, competitive immunoassay

Endocrine Society Clinical Practice Guidelines

• Holick MF. Vitamin D deficiency. New England Journal of Medicine. 2007;357:266–281.
• VITROS Immunodiagnostic Products 25-OH Vitamin D Total Reagent Pack. Publication No. GEM1361_US_EN.
• Holick MF, et al. Evaluation, treatment, and prevention of vitamin D deficiency: An Endocrine Society Clinical Practice Guideline. Journal of Clinical Endocrinology & Metabolism. 2011;96(7).

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