A routine test used to diagnose asthma is significantly more reliable when conducted in the morning, according to new research from the University of Cambridge and Royal Papworth Hospital NHS Foundation Trust. The study, which analysed data from over 1,600 patients, found that lung function tests become less accurate as the day progresses, and are also affected by the season in which they are performed.
Approximately 6.5% of people in the UK—over six years old—suffer from asthma, a condition causing breathing difficulties like wheezing and shortness of breath. Asthma attacks are frequently experienced at night or in the early morning, leading researchers to investigate whether these patterns relate to the body’s natural rhythms – known as circadian rhythms.
The tests in question – spirometry – involve patients exhaling forcefully into a tube to measure lung function. A positive result, indicating possible asthma, is determined by a change in lung function after administering salbutamol, a medication that widens airways.
Researchers accessed data from the Cambridge University Hospitals’ Electronic Patient Record database, allowing them to analyse results from patients referred between 2016 and 2023. After adjusting for factors like age, sex, BMI, smoking history, and initial lung function, they found a clear trend. For every hour passed during the working day, starting at 8:30am, the likelihood of a positive test result decreased by 8%.
“Given what we know about the increased risk of asthma attacks at night and in the early morning, we anticipated some difference in test responses,” explained Dr Ben Knox-Brown, lead research respiratory physiologist at Royal Papworth. “However, the magnitude of the effect was surprising. Performing the test in the morning gives a more reliable representation of a patient’s response to medication, which is crucial for confirming a diagnosis.”
The study also revealed a seasonal component. Individuals were 33% less likely to test positive for asthma in autumn compared to those tested during winter.
Dr Akhilesh Jha, a Medical Research Council clinician scientist, suggests this is because our bodies operate on natural rhythms. “Throughout the day, hormone levels fluctuate, and our immune systems behave differently. These factors could affect test responses,” he said.
We are increasingly seeing evidence that time of day and season significantly impact health and treatment responses, as seen with vaccinations.
