Table 1: Asthma Severity Classification

Table 1: Asthma Severity Classification

Classification	Symptoms	Lung Function
Step 1: Mild-Intermittent	Daytime < 2 times per week Nighttime < 2 times per month Brief exacerbations Asymptomatic between exacerbations Intensity of exacerbations varies	PEF Variability < 20% FEV₁ > 80% PEF > 80%
Step 2: Mild-Persistent	Daytime > 2 times per week but < 1 time per day Nighttime > 2 times per month Exacerbations may affect activity	PEF Variability range of 20% to 30% FEV₁ > 80% PEF > 80%
Step 3: Moderate-Persistent	Daytime symptoms daily Nighttime symptoms > 1 time per week Exacerbations affect activity Exacerbations > 2 times per week Exacerbations last days Daily use of inhaled short-acting ß₂-agonists	PEF Variability > 30% FEV₁ > 60% but < 80% PEF > 60% but < 80%
Step 4: Severe-Persistent	Daytime symptoms continual Nighttime symptoms frequent Symptoms limit physical activity Exacerbations frequent	PEF variability > 30% FEV₁< 60% PEF < 60%

PEF = peak expiratory flow, FEV₁ = forced expiratory volume in 1 second
Adapted from National Asthma Education and Prevention Program. NIH. 1997;97-4051:iii-86.
Kelly HW, et al. Pharmacology: a Pathophysiologic Approach 5th ed. New York: McGraw-Hill; 2002. p. 475-510.

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