Current Methods for Routine Clinical Laboratory Testing of Vitamin D Levels

Requests for vitamin D testing have increased considerably over the past few years, due in part to recent studies that show its association with protecting against skeletal and nonskeletal disorders such as malignancies and metabolic diseases. The Institute of Medicine recently created a consensus report of recommended reference rages and recommended dietary allowances for this vitamin. Two basic categories of laboratory methods exist for analysis of vitamin D; however, their differing methodologies measure a variety of forms and metabolites of vitamin D that may create confusion in interpretation of results. This review of methods considers that total 25-hydroxyvitamin D is the recommended test for vitamin D status and compares methods from published studies and recent findings of proficiency testing surveys. Keywords: vitamin D, 25-hydroxy vitamin D, chemiluminescent immunoassay, high-performance liquid chromatography, radioimmunoassay