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.

◊ This includes current or former smokers with >10 pack year history, those with large amount of biomass fuel exposure, and very high exposures to other indoor or outdoor air pollutants. Refer to UpToDate content on diagnosis and risk factors for COPD for additional information.

§ In selected patients, methacholine challenge may help identify airways hyperresponsiveness in patients with baseline mild-to-moderate airflow limitation, but no bronchodilator reversibility.