Odds for bronchodilator responsiveness lower in afternoon vs. morning hours
Key takeaways:
- Spirometry testing in the afternoon vs. morning was linked to a decreased likelihood for bronchodilator responsiveness.
- The most common reason for spirometry referral in this population was asthma/query asthma.
The odds for bronchodilator responsiveness significantly fell among patients who underwent spirometry testing in the afternoon vs. morning, according to findings published in Thorax.
Additionally, researchers reported that the winter season vs. summer, autumn and spring had the highest proportion of patients who achieved bronchodilator responsiveness.
“Our results highlight the importance of considering the time of day and season of testing when interpreting the results of lung function tests,” Ben Knox-Brown, PhD, lead research respiratory physiologist at Royal Papworth Hospital NHS Foundation Trust, told Healio.
“For clinicians, when asthma is suspected, it would be advantageous to request that the bronchodilator responsiveness test is done first thing in the morning, as our data suggest that this may be a more reliable reflection of a patient's response to inhaled medication,” Knox-Brown said. “This could be particularly important when there is uncertainty around the diagnosis.”
In this cross-sectional study, Knox-Brown and colleagues evaluated 1,620 adults (mean age, 53.2 years; 62% women; 92% white; mean BMI, 29.4 kg/m2) with spirometry data to determine if bronchodilator responsiveness is impacted by time of day (morning vs. afternoon) and season.
The most common reason for spirometry referral in this population was asthma/query asthma (58%), according to the study.
Researchers found a similar proportion of adults with bronchodilator responsiveness when measuring this outcome based on the ATS/ERS definition from 2005 and 2022 (25% vs. 26%). The study highlighted that the 2005 version defined bronchodilator responsiveness as “change in FEV1 or FVC [greater than or equal to] 12% and [greater than or equal to] 200 mL of the initial value,” whereas the 2022 version defined it as “change of [greater than] 10% relative to the predicted value for FEV1 or FVC.”
Within the total cohort, 852 adults had a morning testing time (8:30-12:30), and the remaining 768 adults had an afternoon testing time (13:30-16:30).
Between the morning and afternoon testing groups, researchers reported that bronchodilator responsiveness appeared in the morning group more (ATS/ERS 2005: 28% vs. 22%; ATS/ERS 2022: 28% vs. 23%).
The study went on to find that time per hour increment was significantly linked to bronchodilator responsiveness, observing a lower likelihood for this outcome per 1-hour increment in an age-, sex-, BMI-, baseline FEV1/FVC- and smoking history-adjusted model (aOR using the 2005 and 2022 definitions = 0.92; 95% CI, 0.88-0.97).
Compared with the morning testing group, researchers found that the afternoon testing group faced a significantly decreased likelihood for bronchodilator responsiveness using the 2005 definition (aOR = 0.66; 95% CI, 0.52-0.83) and the 2022 definition (aOR = 0.68; 95% CI, 0.54-0.85).
The study also found that the odds for bronchodilator responsiveness significantly fell among patients with an asthma/query asthma referral tested in the afternoon vs. morning (2005 definition: aOR = 0.69; 95% CI, 0.52-0.93; 2022 definition: aOR = 0.75; 95% CI, 0.56-0.99).
“It is known that diurnal variability in symptom presentation is [a] characteristic of asthma, with previous research suggesting that a biological clock mechanism is responsible for this,” Knox-Brown told Healio. “Even so, we were surprised by the size of the effect we identified, with patients tested in the afternoon 32% less likely to have a positive bronchodilator response compared to those tested in the morning.
“It is reassuring that our real-world data support evidence from lab-based experiments,” Knox-Brown continued.
When assessing differences in bronchodilator responsiveness by season, researchers reported that winter had the highest proportion of adults who achieved this outcome (29% in both definitions), whereas summer ranged from 24% to 25%, autumn ranged from 21% to 25% and spring ranged from 23% to 24%.
Notably, the likelihood for bronchodilator responsiveness per the 2005 definition significantly went down with testing in autumn vs. winter (aOR = 0.67; 95% CI, 0.48-0.92), according to the study. In contrast, the odds for bronchodilator responsiveness per the 2005 and 2022 definitions did not significantly differ between spring vs. winter and summer vs. winter.
“In the future, it is important that prospective studies are conducted to confirm our findings,” Knox-Brown told Healio. “This should ideally be a study where patients are asked to perform bronchodilator responsiveness testing at different times of the day. We are hoping that our study lays the foundation for this research.”
For more information:
Ben Knox-Brown, PhD, can be reached at benjamin.knox-brown@nhs.net.
Reference:
- Routine asthma test more reliable in the morning and has seasonal effects, say doctors. https://www.cam.ac.uk/research/news/routine-asthma-test-more-reliable-in-the-morning-and-has-seasonal-effects. Published March 11, 2025. Accessed March 12, 2025.