Current studies have shown that vitamin D deficiency/insufficiency can result in not only disorders of skeletal system, but maybe nonskeletal diseases as well. Therefore, measurement of 25-hydroxyvitamin D has received more and more attentions clinically. Common methods for 25-hydroxyvitamin D testing include vitamin D binding protein-based competitive assays, immunoassays, high performance liquid chromatography (HPLC), and liquid chromatography-tandem mass spectrometry (LC-MS/MS). Among them, LC-MS/MS is more specific and sensitive and it can measure 25-hydroxyvitamin D3 and D2 individually. However, the methodology is more complicated and its throughput is relatively low. Also, it requires special instrument and operators need additional training. In addition, most LC-MS/MS methods are developed by individual laboratories and they are not very well standardized. Although the specificity of LC-MS/MS method is high, some metabolites may still interfere with the assay. The reference interval of 25-hydroxyvitamin D is still controversial and how to establish gender- and age-specific reference intervals remains debatable. Besides 25-hydroxyvitamin D, whether its metabolites and free 25-hydroxyvitamin D should be measured is still questionable. Although 25-hydroxyvitamin D testing is primarily used for the diagnosis of skeletal diseases, epidemiological studies suggest that vitamin D deficiency/insufficiency may be related to the development and prognosis of nonskeletal diseases. However, more evidence is needed in order to determine the causal relationship between them and the mechanism.
Professor of Pathology and Lab Medicine
Medical Director, Clinical Chemistry
Co-Director, Pathology Core Reference Laboratory and ATL/SPA
Department of Pathology & Laboratory Medicine, Mail Code H160
Penn State University Hershey Medical Center