Saliva as a Matrix for Primary Care: Feasibility and Scoping of its Use for Assessment of Nutrition and Inflammation

Scarce laboratory capacity constrains both primary care and population surveillance for nutritional and inflammation assessment globally. One major contributing factor is the reliance on blood as the primary matrix, and its associated limitations of being invasive, having relatively lower acceptance in apparently healthy individuals and community settings, and being heavily dependent on laboratory and related infrastructure. Saliva offers a non-invasive, inexpensive, and more convenient alternative that causes less discomfort and has the potential to expand the portfolio of point-of-care testing for nutrition and inflammation assessment in primary care. We aimed to synthesize the evidence on the feasibility and scope of using salivary biomarkers for nutrition and inflammation assessment. A literature search was conducted in MEDLINE and CINAHL, without restrictions on language, geographic location, or publication date. Screening and data extraction were done in duplicate on Covidence. A narrative synthesis was done to summarize the results. Seventy-six studies examining salivary biomarkers for nutrition and inflammation were identified across 26 countries, involving 5425 children and 5617 adults. We summarized the results from 33 studies assessing ferritin, iron, zinc, calcium, vitamin A, vitamin B12, vitamin D, vitamin C, and vitamin E in saliva. Additionally, we found 43 studies evaluating salivary inflammatory biomarkers, including C-reactive protein, alpha-1 acid glycoprotein, hepcidin, immunoglobulin A, and cytokines within the context of nutritional impairments. While most biomarker values were detectable in saliva, significant evidence and methodological gaps remain, including the absence of standardized protocols for sample collection, transportation, processing, storage, and laboratory analysis; insufficient information on diagnostic performance, accuracy, and comparability with corresponding blood biomarkers; and challenges in interpreting findings across different population subsets and settings. Future research should focus on improving method reporting and ensuring the clinical relevance of findings to maximize the potential of saliva-based diagnostics for nutrition and inflammation assessment.