Assessment of vitamin D status and definition of a normal circulating range of 25-hydroxyvitamin D

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Abstract
The assessment of circulating 25-hydroxyvitamin D [25(OH)D] for clinical diagnosis has increased in an exponential fashion during the past 5 years. It is thus timely to review the reasons for this increase as well as the diverse analytical methods used to meet this need. Nutritional vitamin D status, as defined by circulating levels of 25(OH)D, has long been implicated in skeletal health. However, in the past decade circulating 25(OH)D has been strongly linked in humans to cancer rates, autoimmune disease, cardiovascular health and infectious disease. As a result, availability and rapid analytical turnaround of 25(OH)D assays have had to improve. Today these demands are largely met in the clinical laboratory by direct automated chemiluminescent platform analysis or high-throughput LC/MS procedures. These methods are diverse and often do not agree with respect to designated reference ranges. The assessment of circulating 25(OH)D levels has become an important clinical tool in the management and prevention of diverse disease states. For this reason, assay standardization as well as a uniform reference range for circulating 25(OH)D levels must be achieved.