Controversies in measuring 25-hydroxyvitamin D

Abstract

There has been an important increase in demand for the laboratory assessment of vitamin D. As a consequence, a number of automated assays have been developed to cope with that demand, replacing manual techniques. Automated assays confront with technical difficulties such as hidrophobic nature of 25- hydroxyvitamin D, multiple related compounds in serum, strong binding to proteins, assay linearity, etc. The use of an International Reference Method, Standard Reference Materials and specific procedures provide the means for manufacturers to accurately standardize their methods. There is no doubt that the latest automated and chromatographic assays have improved their performances, but discrepancies are still present so that each assay must be analyzed carefully. Given the multiple problems affecting the performance of 25- hydroxyvitamin D assays it would be essential that laboratories implement strict quality control procedures. Participation in external quality assessment schemes is also essential and it is recommended that each patient must be followed always at the same laboratory and with the same methodology.