Introduction: Traditionally, vitamin D has been considered almost exclusively related to calcium homeostasis. The era of the pleiotropic effects of vitamin D starts with the discovery of vitamin D receptor in tissues not involved in calcium homeostasis (e.g., skin, placenta, pancreas, breast, prostate and colon cancer cells, activated T-cells). Animal and clinical studies indicate that vitamin D deficiency could be linked to several chronic diseases, including cardiovascular, autoimmune disease and cancer. Recently it is estimated that vitamin D deficiency is a global health problem. Over a billion people worldwide and 66% in Bulgaria are vitamin D deficient or insufficient. A reliable evaluation of vitamin D status by measuring the circulating 25-hydroxy vitamin D levels (25OHD) is needed for making decision for vitamin D supplementation.
Aim: To study the literature in web databases regarding the analytical methods for accurate and robust determination of circulating vitamin D serum levels.
Results: Immunoassays and protein binding assays can only report the total concentration of 25OHD (D2 and D3) in blood plasma. They can be used for routine screening of circulating vitamin D levels.
Chemical assays (HPLC-UV, LC-MS/MS, GC-MS) are the most accurate, selective and specific for both 25OHD2 and 25OHD3. LC-MS/MS is considered as reference method for measuring 25OHD2/D3 levels.
Conclusion: There is no standardized 25OHD assay to arbitrarily establish the `deficient` threshold of 75 nmol/L and to provide clinicians with accurate tool to diagnose vitamin D hypovitaminosis and to make decision for supplementation.
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