In-House Test Menu Expanded to Include Vit D
LabDx is pleased to announce that effective January 3rd, the analysis of Vitamin D, 25 Hydroxy (Vit D-25 OH) will be performed in our laboratory. This assay will report a total quantitative Vit D-25OH value. This assay will be performed Monday – Friday with results available the next day.
Specimen Requirements
1.0 ml Serum from a Red Top or SST is the preferred sample. Blood should be collected by venipuncture and allowed to clot for a minimum of 30 minutes and centrifuged. Serum should be separated from the clot as soon as possible. If not analyzed within 48 hours, the specimen should be kept refrigerated.
Background
Over the past 20 years our understanding of the metabolism and mechanism of action of vitamin D has become clearer. Vitamin D is a commonly used collective term for a family of closely related seco-steroids involved in calcium and phosphorous homeostasis. In addition to its effect on calcium homeostasis, several active forms of Vitamin D posses a variety of non-calcaemic functions. These include: regulation of cell differentiation and proliferation, a potent inhibitor of cellular growth, stimulator of insulin secretion, modulator of immune function and inhibitor of rennin production.
Advantages of measuring Vitamin D, 25 Hydroxy
Quantitation of serum Vit D-25OH provides a clinically useful assessment of an individual’s vitamin D stores over long periods due to its rather long half-life. Also, it has been shown that the liver production of Vit D-25OH is not significantly regulated and is primarily dependent on substrate concentration available in the body. Given the fact that fortification of milk and preparation of multivitamins are now prepared with both forms, Vitamin D2 and Vitamin D3, separate measurement of the metabolites is of little value.
Expected Values
A review of the literature suggests the following ranges for evaluation of Vitamin D, 25 Hydroxy status.
| Vitamin D status | Vitamin D, 25 Hydroxy |
| Deficiency | Less than 20 ng/ml |
| Insufficiency | 20ng/ml – 29 ng/ml |
| Sufficiency | 30 ng/ml – 50 ng/ml |
| Potential Toxicity | Greater than 100 ng/ml |
Note: Pediatric and gender reference ranges have not been established
References:
1. Institute of Medicine (IOM) 2011 Report, J Clin Endocrinol Metab, January 2011
2. Zerwekh, J.E., The Measurement of vitamin D: analytical aspects, Ann Clin Biochem 2004: 41: 272-281
3. Hart, G.H., Review Series, Volume 1, Sept 2004, Immunodiagnostic Systems (IDS)