The goals of this observational study are to identify factors independently associated with admission eosinopenia in patients with a severe exacerbation of chronic obstructive pulmonary disease (COPD) and to determine when blood eosinophil count (BEC) will recover to baseline stable state in patients who are admitted to hospital with a severe exacerbation of COPD and associated eosinopenia.

The main aims of the study are to:

1. Identify demographic, physiological and clinical factors independently associated with admission eosinopenia in patients with a severe exacerbation of COPD
2. Assess the time to recovery from eosinopenia to stable BEC following a severe exacerbation of COPD

Blood eosinophils are a type of white blood cell that play a role in the immune system including fighting infection. They have numerous roles but are primarily involved in inflammation. They are recruited from the blood into sites of inflammation.

The blood eosinophil count (BEC) can be used as a biomarker to predict whether the addition of inhaled corticosteroid (ICS) to long-acting bronchodilators (LABD) will be beneficial in reducing future COPD exacerbations. This association is based on BEC being measured when patients are clinically stable. Patients with a higher BEC are more likely to gain these benefits where as conversely, patients with a lower BEC are less likely to benefit and the risk of side effects such as pneumonia will likely outweigh any potential benefit. Current national and international COPD guidelines suggest the use of BEC as a biomarker to help inform the decision of whether to commence or withdraw ICS, but do not specify measuring BEC at a time of clinical stability.

Decisions regarding changes to management are often made in the acute setting. Eosinophils transiently drop to very low levels in half of patients who are admitted to hospital with exacerbations of COPD. Measuring BEC during an acute illness risks incorrectly identifying all patients who may benefit from the introduction of an ICS. In the current BEC COPD study, reliance on admission and discharge BEC inappropriately denied ICS to 47% and 33% of patients respectively compared to a confirmed stable-state measure.

There are co-primary aims for this study. Firstly, the investigators wish to determine when BEC will recover to stable state following a hospital admission for exacerbation of COPD. Determining this will inform healthcare professionals of the optimum time to measure BEC for use as a biomarker when making decisions related to management escalation. Based on the results of BEC COPD, it is likely that an increased number of patients will be identified as being above the BEC threshold and therefore likely to benefit from ICS when time is allowed for BEC to recover to stable state. Appropriate introduction of ICS in this patient group will reduce exacerbation and hospital re-admission rates and thus may reduce overall mortality within this high-risk group. This should reduce the burden of COPD on patient's health, quality of life and the NHS.

Eosinopenia during severe exacerbation of COPD is associated with increased in-hospital and one year mortality. Treatment with oral corticosteroids does not fully explain the mechanism behind the development of eosinopenia, with the phenomenon being less common on discharge compared to admission despite inpatient oral corticosteroid treatment. The investigators other co-primary aim is to identify demographic, physiological and clinical factors independently associated with admission eosinopenia in patients with a severe exacerbation of COPD, providing useful mechanistic information regarding the relationship between BEC and short-term mortality.

The hypothesis for this study is that 90% of participants who are admitted to hospital with a severe exacerbation of COPD and eosinopenia will have recovery of their BEC to baseline stable state within 4 weeks. The investigators also hypothesize that there are demographic, physiological and clinical factors independently associated with admission eosinopenia other than prior systemic corticosteroid use.

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.

Participants will be aged 35 years and over. They will have been admitted to hospital with an exacerbation of COPD +/- eosinopenia.