Use of PFTs to diagnose asthma in adults and adolescents

BD: bronchodilator; FEV₁: forced expiratory volume in one second; FVC: forced vital capacity; LLN: lower limit of normal.

* If spirometry pre- and post-BD or bronchoprovocation challenge is not available, serial peak flow measurements showing a variability of ≥20% that corresponds to symptoms is suggestive of asthma.

¶ Patients with borderline airflow limitation (FEV₁/FVC <70% or LLN, but FEV₁ ≥80% predicted) may have asthma, but will need further monitoring over time to confirm. Refer to UpToDate content on the diagnosis of asthma.

Δ Positive methacholine: A decrease in FEV₁ by ≥20% (PC20) after inhalation of 8 mg/mL or less is considered positive; a PC20 ≥16 mg/mL is considered negative. Positive mannitol: Decrease in FEV₁ by ≥15% after total cumulative dose of ≤635 mg. Positive exercise challenge; decrease in FEV₁ by ≥10%, although ≥15% is more diagnostic.