Comparison of passive drool and cotton-based collection methods for salivary C-reactive protein measurement

Saliva collection and handling procedures for salivary C-reactive protein (CRP) can be challenging due to a lack of standardized protocols. This study compared two collection methods used to quantify salivary CRP. Twenty-two Chinese adults provided two unstimulated whole saliva samples using passive drool and cotton-based collection devices in two consecutive mornings at baseline and 1 month later. The effects of various factors on CRP levels were analyzed using linear mixed models. Salivary CRP levels were significantly affected by collection time and method, but not day or wave. The CRP peaked upon awakening and declined 45 min later. CRP levels were significantly higher in the passive drool than in the cotton-based method. The Bland-Altman plot revealed relative and proportional biases. The difference in the CRP levels between the methods decreased as the CRP levels increased. Results suggest that passive drool and cotton-based collection methods should not be used interchangeably for measuring low levels of salivary CRP.