Are Results of Bronchodilator Testing Affected by Time of Day or Season?

Asthma symptoms often worsen at night, but we know less about how timing of pulmonary function testing affects results for people with asthma. In a retrospective U.K. study, researchers analyzed results from 1620 adults who underwent spirometry before and after a bronchodilator challenge; 58% were referred specifically for suspected asthma.

In an hour-by-hour analysis, patients were significantly more likely to have positive bronchodilator responses (i.e., change of >10% relative to the predicted value for forced expiratory volume in 1 second [FEV₁] or forced vital capacity (FVC) after bronchodilator administration) early in the morning; with each passing hour before testing, there was small decrease (8%) in likelihood of a positive response…