Saliva Collection Methods and Storage Conditions Affect Salivary Iodine Concentration: Recommendations for Optimal...

Salivary iodine concentration (SIC) has been demonstrated to apply to iodine nutrition assessment. However, limited research exists on saliva collection and storage methods, which are essential for reliable measurements of SIC.

This study aims to investigate the effects of various saliva sample collection and storage methods and to establish standardized protocols.

Healthy adults were randomly recruited from the university. This study was designed with 2 components: collection methods and storage conditions. Participants provided 4 saliva samples each under stimulation and mouthwash conditions for the collection method analysis. Regarding storage conditions, a 5-mL saliva sample was collected and divided into 4 portions. One portion underwent analysis within 24 h, whereas the remaining 3 were stored at -80°C, -20°C, and 4°C, respectively. SIC detection was performed after 7, 90, 180, and 365 d of storage.

Compared with natural secretion, SIC significantly decreased by 21.44 μg/L [95% confidence interval (CI): -33.74, -9.14] after olfactory stimulation, by 17.74 μg/L (95% CI: 26.06, -9.43) after mechanical stimulation, by 74.37 μg/L (95% CI: -85.31, -63.44) after chewing stimulation, and by 23.90 μg/L (95% CI: -31.00, -16.79) 1 min after rinsing. No significant change was observed after rinsing for 5 and 10 min (P > 0.05). Compared with timely testing, SIC remained stable at -80°C for 365 d (all P > 0.05). However, at -20°C, SIC significantly decreased by 20.8 μg/L (95% CI: -37.7, -3.79) after 180 d, and by 26.9 μg/L (95% CI: -43.9, -9.81) after 365 d. At 4°C, SIC significantly increased by 25.8 μg/L (95% CI: 5.49, 46.2) after 365 d.

This study recommends collecting saliva through natural secretion 5 min after rinsing. For long-term storage (≥180 d), samples should be preserved at -80°C. For short-term storage (≤90 d), they may be stored at -80°C, -20°C, or 4°C.