Saliva is increasingly promoted as a suitable alternative diagnostic bio-sample to blood, yet its role in respiratory disease is still to be elucidated.
Salivary levels of C-Reactive Protein (CRP), Procalcitonin (PCT) and Neutrophil Elastase (NE) were assessed in patients with COPD to determine if saliva could provide an alternative diagnostic bio-sample to blood. As the clinical usefulness of biomarkers relies on correlation to patient events, we also explored the relationship between target saliva analyte levels and wellbeing scores on breathing and activities of daily living (ADL), recorded in a purposeful diary.
The study included 139 subjects: 17 healthy non-smokers; 24 healthy smokers; 98 patients with COPD [Global Initiative for Chronic Obstructive Lung Disease (GOLD) Stage I, 16; Stage II, 32; Stage III, 39; Stage IV, 11]. Participants were assessed over 3 visits, one week apart and involving patient completion of a self-assessment diary, spirometry and, saliva sampling. 22 randomly selected COPD subjects provided simultaneous blood samples. Each salivary biomarker could distinguish across the 3 health status groups; however when adjusted for confounding factors this significance only remained for salivary NE, which was increased in healthy smokers compared to healthy non-smokers (p < 0.001) and stable COPD subjects (p < 0.001). Patients with an acute exacerbation of COPD (n = 36) had a median increase in all 3 salivary biomarkers (p < 0.001). CRP: median 5.74 ng/ml,[interquartile range 2.86–12.25], (95% Confidence Interval (CI): 3.72–11.47); PCT 0.38 ng/ml, [0.22–0.94], (95% CI: 0.31–0.54) and NE 539 ng/ml [112.25–1264], (95% CI: 169–982). Salivary CRP and PCT concentrations strongly correlated with their serum counterparts; salivary NE did not. Salivary CRP and PCT levels correlated with breathing scores (r = 0.14, p < 0.02; r = 0.13, p < 0.03 respectively) but not with activities of daily living. Salivary NE showed no relationship to wellbeing scores.
Salivary CRP, PCT and NE provide clinically relevant information on disease status in COPD, and additionally NE on smoking status in healthy individuals. These results provide the conceptual basis for saliva to be used as a bio-sample in COPD monitoring.