Saliva: challenges, possibilities, and limits of the diagnostic use: Part 2 – Pre-analytical and analytical aspects

Part I of this review was dedicated to the biological complexity of saliva and its relationship with the pathophysiology of many organs. In Part II, issues related to the pre-analytical and analytical phases are illustrated, focusing first the attention on the main sources of variability, starting from the few data available on biological variation to the different approaches for sample collection under basal or stimulated conditions. Up to now, published data, obtained on small groups of healthy or diseased individuals, seem to be indicative of wide pre-analytical errors and/or individual variability. The established clinical use of salivary tests is then reviewed and a series of possible new applications are presented. Methodologies employed in saliva are presented, ranging from commonly applied techniques, such as colorimetric enzymatic methods and ELISA, to more sophisticated technologies (gas chromatography–mass spectrometry, liquid chromatography-mass spectrometry and 1H NMR spectroscopy) to investigate proteomics and metabolomics. The aim of this review is to present the pre-analytical issues related to its collection and storage and to illustrate the knowledge gaps and the numerous opportunities that the analysis of this interesting biological fluid may offer.