Classification of Asthma Severity

 
Clinical Features Before Tx
  Days with Sx Nights with Sx PEF or FEV1* PEF Variability
Step 4
Severe Persistent		 Continual Frequent <= 60% > 30%
Step 3
Moderate Persistent		 Daily =>  5 months > 60-80% > 30%
Step 2
Mild Persistent		 3-6 per week 3-4 per month => 80% 20 - 30%
Step 1
Mild Intermittent		 <= 2 per week <= 2 per month => 80% < 20%
*Percent predicted value for forced expiratory volume in one second (FEV1) and percent of personal best for peak expiratory flow (PEF), relevant for children above 6 who can use a peak flow meter.
  • Patients should be assigned to the most severe step in which any feature occurs.  Clinical features for individual patients may overlap across steps.
  • An individual's classification may change over time.
  • Patients at any level of severity of chronic asthma can have mild, moderate, or severe exacerbations of asthma.  Some patients with intermittent asthma experience severe and life-threatening exacerbations separated by long periods of normal lung function and no symptoms.
  • Patients with two or more asthma exacerbations per week (i.e., progressively worsening symptoms that may last hours or days) tend to have moderate-to-severe persistent asthma.

This page is based on the Practical Guide for the Diagnosis and Management of Asthma, a publication of the National Heart, Lung and Blood Institute of the National Institutes of Health of the United States
NIH Publication No. 97-4053, October 1997

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