Can we accurately measure the concentration of clinically relevant vitamin D metabolites in the circulation? The problems and their consequences.

Increased interest in vitamin D measurements in clinical studies has contributed to the development in recent years of several new immunochemical assays (manual and for automatic analyzers). New methods, including HPLC (high performance liquid chromatography), and LC-MS/MS (liquid chromatography coupled with tandem mass spectrometry) have also been introduced into routine diagnostic laboratories. Because of the variety of assays and methods used, the question arises which one is the most accurate for the measurement of vitamin D metabolites concentration. In this review, we summarise the advantages and disadvantages of these methods, describe the complexity of vitamin D metabolites pattern in the circulation, and discuss the problem of accurate measuring its concentration.