Abbreviations: FEV₁, forced expiratory volume in 1 second; FVC, forced vital capacity.

^aNormal FEV₁/FVC: 8-19 yr, 85%; 20-39 yr, 80%; 40-59 yr, 75%; 60-80 yr, 70%.

^bFor treatment purposes, patients who had ≥2 exacerbations requiring oral systemic corticosteriods in the past year may be considered the same as patients who have persistent asthma, even in the absence of impairment levels consistent with persistent asthma.

Adapted from NIH Guidelines for the Diagnosis and Management of Asthma; 2007.