A Pilot Study to Characterise Saliva and Sputum FTIR Spectral Profiles in Patients with COPD During Exacerbations and When Stable

Inclusion Criteria: * Participants with a confirmed diagnosis of an exacerbation of COPD (aged ≥40 years), n=40 (20 participants recruited in phase 1 and 20 participants recruited in phase 2) who are able to spontaneously expectorates sputum during exacerbations and on at least 3 out of 7 days when well. * Able to provide written informed consent Exclusion Criteria: * Participants with other significant respiratory disease that, in the opinion of the clinical investigator, is the major cause of their respiratory symptoms (e.g. pulmonary tuberculosis, allergic bronchopulmonary aspergillosis, pulmonary fibrosis). * Participants with COPD whose deterioration in respiratory symptoms is not thought to be due to an exacerbation of their COPD (e.g. pneumonia\*, pneumothorax, pulmonary embolus). * A member of the research study medical team will review the participant's chest X-Ray (CXR) to exclude any pneumonia, defined by consolidation on CXR before they are recruited onto the study if a CXR has been taken. In participants who have not had a CXR, exclusion of pneumonia will be based on clinical assessment.