Eosinopenia in Severe COPD Exacerbation

Inclusion Criteria: * Admitted to hospital with primary clinical diagnosis of exacerbation of COPD\* * Smoking history of at least 10 pack years * Airflow obstruction: FEV1/FVC ratio \< 0.7 confirmed on historic or inpatient spirometry * Capacity to give informed consent to participate Exclusion Criteria: * Parasitic infection, systemic fungal infection (excluding infection limited to nails or skin), eosinophilic granulomatosis with polyangiitis, hypereosinophilic syndrome or other conditions associated with a high eosinophil count# * Active malignancy * Maintenance oral prednisolone or other systemic steroids, anti-interleukin 5 therapy or other medication known to influence eosinophils * Patients with poor venous access * Investigator confirmed history of asthma * Non-COPD related health problems which in the view of the primary investigator may compromise the conduct and completion of the study ADDITIONAL CRITERIA FOR THE TIME TO RECOVERY FROM EOSINOPENIA ANALYSIS ONLY Inclusion criteria: * Eosinopenia on admission * Uneventful recovery\* * Eosinopenia on admission who do not receive a further course of systemic corticosteroids or require emergency hospital admission for an acute illness in the six weeks following admission to hospital with a severe exacerbation of COPD.