Asthma Bronchodilator Tests May be More Reliable in the Morning

Ben Knox-Brown, PhD

Credit: ResearchGate

New research has found that bronchodilator responsiveness was highest in the morning and decreased throughout the day, potentially informing asthma testing strategies.1

“Given what we know about how the risk of an asthma attack changes between night and day, we expected to find a difference in how people responded to the lung function test, but even so, we were surprised by the size of the effect,” lead investigator Ben Knox-Brown, PhD, Royal Papworth Hospital NHS Foundation Trust, Cambridge, United Kingdom, said in a statement.2 “This has potentially important implications. Doing the test in the morning would give a more reliable representation of a patient's response to the medication than doing it in the afternoon, which is important when confirming a diagnosis such as asthma.”

Knox-Brown and colleagues analyzed data from 1620 patients in CUH’s Electronic Patient Record Research and Innovation (ERIN) database referred between 2016 and 2023. They found that per 1-hour increment in the working day, the odds of having bronchodilator responsiveness declined by 8% (odds ratio [OR], 0.92; 95% CI, 0.88-0.97). When comparing morning to afternoon, participants also had reduced odds of bronchodilator responsiveness in the afternoon (OR, 0.68; 95% CI, 0.54-0.85). This association remained positive for patients referred for asthma/query asthma and was not seen in those reffered for other reasons. The investigators also found a significant interaction between referral reason and time of day (per 1-hour increment) on the odds of having a positive bronchodilator response (p value for likelihood ratio test <.001).1

The investigators also looked at seasons and bronchodilator responsiveness and found that a greater proportion of patients tested in the winter had bronchodilator responsiveness compared with other seasons. Compared with those tested in winter, patients tested in autumn had significantly lower odds of having bronchodilator responsiveness but only for those with bronchodilator responsiveness according to the ATS/ERS 2005 definition (OR, 0.67; 95% CI, 0.48-0.92).1

“Our bodies have natural rhythms – our body clocks,” Jha said. “Throughout the day, the levels of different hormones in our bodies go up and down and our immune systems perform differently, for example. Any of these factors might affect how people respond to the lung function test,” investigator Akhilesh Jha, MBBS, Medical Research Council Clinician Scientist, University of Cambridge and Honorary Consultant in Respiratory Medicine at Cambridge University Hospital added.2

“The idea that the time of day, or the season of the year, affects our health and how we respond to treatments is something we’re seeing increasing evidence of. We know, for example, that people respond differently to vaccinations depending on whether they’re administered in the morning or afternoon. The findings of our study further support this idea and may need to be taken into account when interpreting the results of these commonly performed tests,” Jha said.2

The investigators noted that prospective studies should be conducted to confirm their findings with repeated measurements of the same individuals at different times of the day.

REFERENCES

1. Knox-Brown B, Kon FC, Sylvester KP, Jha A. Effect of time of day and seasonal variation on bronchodilator responsiveness: the SPIRO-TIMETRY study. Thorax. Published online March 11, 2025. doi:10.1136/thorax-2024-222773

2. Routine asthma test more reliable in the morning and has seasonal effects. News release. University of Cambridge. March 12, 2025. https://www.cam.ac.uk/research/news/routine-asthma-test-more-reliable-in-the-morning-and-has-seasonal-effects