Other investigations

Further tests include:

• sputum may reveal:
  • the infective organism that triggered the acute attack
  • eosinophilia
  • Curschmann's spirals (casts of small airways)
    
    
• FEV1/FEV:
  • usually less than 75%
  • improves with bronchodilator administration
  • there is usually a fall in FEV with exercise
    
    
• blood culture - consider if infection has caused the exacerbation
  
  
• hypersensitivity skin tests:
  • are not performed in the acute phase
  • may identify allergy to specific antigens, e.g. aspergillus, and so be helpful in guiding treatment
    
    
• autoantibodies, particularly ANCA if Churg-Strauss syndrome is suspected