The role of tandem mass spectrometry in clinical chemistry: quantification of steroid hormones and vitamin D

Nowadays tandem mass spectrometry coupled to liquid chromatography is considered as the "gold standard" technique for steroid hormones quantification in biological fluids. Its emerging role in the clinical laboratories is mainly due to its capability to overcome the main limitations of the widespread immunoassays (IAs), providing, at the same time, the simultaneous quantification of several steroids of interest. This is a very important feature, as it allows, just in a single analysis, the monitoring of some key steroids in a metabolic pathway. In this chapter, we will describe the instrumental layout to be used in the measurement of clinically relevant steroids or steroid panels, and we will discuss the advantages and disadvantages of tandem mass spectrometry with respect to the main IA-based assays. The quantification of the main metabolites of vitamin D, 25-hydroxyvitamin D3, which is considered a steroid hormone, is also discussed in the chapter. Applications concerning 11β-HSD enzyme activity, 21-hydroxylase deficiency in newborns, hypovitaminosis D in patients with heart failure and vitamin D intoxication are discussed.