How to diagnose asthma and determine the degree of severity of the disease.

Asthma care begins with establishing the diagnosis and determining the severity of the disease. The key elements are the history of the disease and the measurements of peak expiratory flow (PEF). The characteristic of asthma is variability. A history of chest symptoms that are variable is typical of asthma. Demonstrating a variation of PEF > or = 20% establishes a definite diagnosis of asthma. This variability is demonstrated either, in patients with normal PEF when they are well, by measuring a decrease in PEF during a period when the patient has symptoms of asthma or, in patients with PEF < normal, an improvement after inhalation of salbutamol or after a period of treatment. Classifying the severity of asthma is also based on history and lung function measurement. Patients with PEF <60% or continuous symptoms are classified as severe persistent. Those with PEF 60-79% or daily symptoms (not continuous) are classified as moderate persistent. Those with symptoms more than once per week but less than daily and PEF > or = 80% are classified as mild persistent. Those with symptoms less than once per week and PEF > or = 80% are classified as intermittent. Establishing the diagnosis and assessing the severity are crucial to high quality care.