Diagnosis

• In adults >16:

  1. Measure blood eosinophil count or FeNO - diagnose asthma if eosinophil count raised or FeNO level 50 ppb or more
  2. If asthma not confirmed with eosinophil or FeNO level, measure bronchodilator reversibility with spirometry - diagnose asthma if the FEV1 increase is 12% or more and 200ml or more from pre-bronchodilator measurement
  3. If spirometry not available measure PEF twice daily for 2 weeks - diagnose if PEF variability 20% or more
• When the airways become inflamed, cells involved in the inflammatory response, such as eosinophils and mast cells, release signaling molecules that stimulate the production of NO