Effect of diabetes mellitus type 2 on salivary glucose, immunoglobulin A, total protein, and amylase levels in adults: A systematic review and meta-analysis of case–control studies

BACKGROUND: Saliva is a fluid with the complex compound which can be used as diagnostic markers for type 2 diabetes (T2D). This meta-analysis evaluated salivary glucose, immunoglobulin A (IgA), total protein, and amylase levels in adult T2D compared with the controls as well as the correlation of salivary glucose levels with serum glucose and hemoglobin A1C (HbA1c) levels in both groups. MATERIALS AND METHODS: Web of Science, Scopus, PubMed, and Cochrane Library databases were searched up to July 2017. A random-effects analysis was performed using the mean difference (MD) and 95% confidence intervals. The search terms were “T2D, IgA, amylase, total protein, or glucose” combination with “saliva.” The studied variables were the sample size, the percentage of male, the mean age, the condition of saliva sampling, and the salivary levels of mentioned factors. RESULTS: A total of 25 studies were included in this meta-analysis with 1432 and 900 diabetic patients and healthy controls, respectively. MD of salivary glucose level in patients with T2D, compared with the healthy controls, in fasting and nonfasting conditions were 6.23 mg/dL (P = 0.0002) and 6.70 mg/dL (P < 0.00001), respectively. Furthermore, the fasting salivary total protein in the patients was significantly higher than the controls (MD = 167.96 mg/dL; P = 0.03). Non-fasting salivary amylase and secretory IgA levels were significantly lower in the patients (MD = −48.61 IU/mL; P < 0.00001) than in the controls (MD = −9.42 IU/mL; P = 0.0006), respectively. The pooled estimate showed a significant correlation between salivary and serum glucose in the patients (r = 0.765; P < 0.001) and the controls (r = 0.646; P < 0.001) and between salivary glucose and serum glycated hemoglobin in the patients (r = 0.721; P < 0.001). CONCLUSION: Measurement of these salivary factors can be helpful for diagnostic and monitoring purposes of T2D. In addition, salivary glucose as a diagnostic tool can evaluate serum glucose and HbA1c levels in the diabetic patients.