Abstract

Excessive salivary contamination of induced sputum samples prevents the satisfactory examination of lower airway inflammation. The effects of salivary contamination on different sputum fluid phase measures and the levels of salivary contamination preventing analysis are not defined. The present study sought to examine this by investigating the effect of increasing salivary contamination on induced sputum samples. Sputum and saliva samples from subjects with asthma and healthy controls were collected, and treated with dithiothreitol (DTT). Saliva was then added to aliquots of dispersed sputum in increasing proportions (0% to 100%). The effect of increasing saliva contamination was assessed on sputum total cell count, viability, differential cell count and fluid phase levels of interleukin (IL)-8, eosinophil cationic protein (ECP) and total protein. The addition of saliva to induced sputum reduced total cell counts and absolute cell counts but did not change the differential cell count. Levels of fluid phase ECP and IL-8 were significantly reduced with increased salivary contamination. There was a progressive reduction in ECP and IL-8, which reached significance at 70% and 80% saliva contamination, respectively. IL-8 levels corrected for total protein showed no change with increasing saliva concentrations. Induced sputum differential cell counts expressed as the proportion of nonsquamous cells are robust measures that are not influenced by salivary contamination. Studies reporting total and absolute cell counts and fluid phase mediator levels require control for squamous contamination.