Saliva as a Diagnostic Tool: The Future of a Non-invasive Disease Detection

Abstract

^{Saliva is an easily accessible biological fluid that has gained increasing attention as a potential diagnostic specimen. In addition to its well-established roles in lubrication, digestion, taste and protection of the oral cavity, saliva contains proteins, enzymes, hormones, antibodies, nucleic acids, metabolites and microbial components that may reflect physiological and pathological changes. These characteristics have encouraged investigation of saliva as a non-invasive source of biomarkers for both oral and systemic diseases. Salivary diagnostics has been explored in endocrine disorders, cardiovascular diseases, diabetes mellitus, infectious diseases, malignancies and periodontal disease. The presence of cell-free DNA, RNA, microRNA, proteins, metabolites and extracellular vesicles has also led to the concept of saliva as a potential liquid-biopsy medium. Its painless collection and suitability for repeated sampling make it particularly attractive for screening and point-of-care applications.  This narrative review discusses the composition and physiological functions of saliva and summarizes its emerging diagnostic applications in cardiovascular disease, endocrine disorders, oral cancer, diabetes mellitus, dental caries and periodontal disease. Although numerous biomarkers have demonstrated promising associations with disease, differences in sample collection, salivary flow, oral health, medications, diet and analytical methods remain important limitations. Further prospective studies, standardized protocols and validated diagnostic thresholds are necessary before most salivary biomarkers can be incorporated into routine clinical practice. With continued advances in molecular diagnostics, biosensors and point-of-care technologies, saliva may become an important component of non-invasive and personalized healthcare.}