# Unstimulated Parotid Saliva Is a Better Method for Blood Glucose Prediction
###### Abstract  
Objective: Saliva glucose has been widely used in diagnosing and monitoring diabetes, but the saliva collection method will affect saliva glucose concentration. So, this study aims to identify the ideal saliva collection method. Method: A total amount of six saliva collection methods were employed in 80 healthy participants in the morning. Besides, three unstimulated saliva methods were employed in another 30 healthy participants in the morning; in the meantime the blood glucose of these 30 participants was detected with a Roche blood glucose meter. The glucose oxidase method with 2, 4, 6-tribromo-3-hydroxybenzoic acid (TBHBA) as the chromogen has been improved to be suitable for healthy people, through the selection of the optimal pH value and ionic strength of the reaction system. This method was used for the detection of saliva glucose. Results: The improved method obtained absorbance at the wavelength of 520 nm, and the optimized parameter combination was pH 6.5 and 5 mg/dL NaCl. The lower limit of glucose detection was 0.1 mg/dL. Unstimulated saliva glucose concentration was higher than stimulated saliva glucose concentration. Unstimulated parotid saliva glucose concentration was the highest. Besides, unstimulated saliva glucose has a better normal distribution effect. Meantime, it was found that unstimulated parotid saliva was the most highly correlated with blood glucose (R\({}^{2}\) = 0.707). Conclusions: the saliva collection method was an important factor that affected saliva glucose concentration. Unstimulated parotid saliva was the most highly correlated with blood glucose, which provided a reference for prediction of diabetes mellitus. Keywords:saliva; glucose; methods; diabetes mellitus; sample collection +
Footnote †: journal: Medical Engineering, Tsinghua University, Beijing 10084, China  
for the detection and monitoring of DM. [PERSON] et al. [9] pointed out that saliva, like blood, can reflect changes in human physiological functions, so it may be a substitute for early detection and monitoring of DM. Meanwhile, saliva collection is convenient, safe, non-invasive, with no risk of infection, and painless to patients. Therefore, people pay more and more attention to it in experimental research and clinical use [10; 11]. Although saliva glucose reflects the health of the human body, its use as a diagnostic fluid has been hindered and neglected, mainly because of the lack of standardized saliva collection methods [12; 13]. Most studies use saliva in diagnosis using different collection methods and often lack clear sampling processes [14; 15]. This makes it difficult to compare the results of different studies [16]. In general, most studies view saliva incorrectly as a homogeneous body fluid. However, saliva is not a solitary fluid and cannot be viewed as such. Instead, it is a complex mixture consisting of the secretions of three main glands (parotid, submandibular, and sublingual), each of which secretes a characteristic type of saliva, along with hundreds of small salivary glands, gingival crevicular fluids and debris [17]. It is also unstable, but constantly changing, and its composition is affected by other factors such as sampling method, environment, oral hygiene, psychological status and general health [18]. Thus, it is necessary to establish precise standards for saliva collection [19], such as the type of saliva glucose, i.e., saliva produced by whole saliva or specific glands, and whether the sample was collected after stimulation [20; 21]. Besides, most of the carbohydrates that are present in saliva are either synthesized in situ in the salivary glands and/or transported from blood capillaries into saliva by diffusion, active transport and/or ultra-filtration [22]. The glucose in saliva may also undergo modifications due to underlying pathological conditions and/or as a result of exposure to drugs and other compounds or solutions.