C-Reactive Protein in Saliva as a Non-Invasive Marker of Metabolic Syndrome: A Systematic Review and Meta-Analysis

Metabolic syndrome (MetS) is a global health concern characterized by a cluster of metabolic abnormalities, including central obesity, hypertension, hyperglycemia, and dyslipidemia, which increase the risk of cardiovascular disease and type 2 diabetes. This systematic review and meta-analysis aimed to assess the diagnostic value of salivary C-reactive protein (CRP) as a non-invasive biomarker for MetS. A comprehensive search of PubMed, Cochrane Library, and Web of Science was conducted through December 2024. Eligible studies reported salivary CRP levels in individuals with and without MetS. Two independent reviewers extracted data on study design, demographics, CRP measurement methods, and diagnostic criteria for MetS. Meta-analyses were performed using random-effects models to calculate pooled standardized mean differences (SMDs) with 95% confidence intervals. Among 863 records screened, 19 studies involving 3,157 participants met the inclusion criteria. The pooled results showed significantly higher salivary CRP levels in individuals with MetS compared to controls (Hedges’ g = 1.02; 95% CI: | 0.23, 1.81] P = 0.01). High between-study heterogeneity was observed (I² = 98.91%, P < 0.001), and funnel plot asymmetry suggested potential publication bias or underlying heterogeneity. These findings suggest that salivary CRP may serve as a promising non-invasive biomarker for detecting metabolic syndrome.