The (Sun)Light and Dark of 25-Hydroxyvitamin D Testing

Background: Vitamin D is obtained by the body via sunlight on the skin, from the diet, or from supplementation. The primary function of vitamin D is to maintain calcium homeostasis and bone health, but in the past decade, numerous other health benefits have been proposed. Content: With the increased awareness of the potential benefits of maintaining sufficient concentrations of 25-hydroxyvitamin D, clinicians began ordering this test for their patients much more frequently. The number of available methods increased, but with that came a larger focus on the challenges of measuring 25-hydroxyvitamin D accurately due to binding to vitamin D-binding protein and the presence of other vitamin D metabolites. Further, standardization of these assays became a focus for several organizations so that clinical guidelines can be applicable to every patient regardless of what methodology is used in 25-hydroxyvitamin D measurement. Summary: Improvements are being made in the specificity, accuracy, and standardization of the measurement of 25-hydroxyvitamin D, and the future of this testing is looking brighter.