A new study has found that the results of a lung function test, commonly used to help diagnose asthma, can vary according to the time of day and season of the year.
Researchers at the University of Cambridge showed that positive bronchodilator response (BDR) was more likely to occur in the morning and gradually decreased throughout the day. In addition, positive BDRs were also more frequently observed during winter compared to the rest of the year. The findings are published in Thorax.
Around 6.5 per cent of people over the age of six are affected by asthma in the UK. Most asthma attacks occur at night-time or early in the morning and could be linked to the body’s circadian rhythms. The researchers wanted to explore whether the body’s internal clock could impact our ability to diagnose asthma.
The study retrospectively analysed data from 1,620 patients referred to Cambridge University Hospitals NHS Foundation Trust (CUH) between January 2016 and December 2023. All participants were over 18, with an average age of 53.2, and had acceptable and reproducible prebronchodilator and postbronchodilator spirometry using the MasterScreen-PFT-Pro device.
BDR was defined for both the American Thoracic Society/European Respiratory Society (ATS/ERS) 2005 criteria (change in FEV1 or FVC≥12% and ≥200 mL of the initial value), and the ATS/ERS 2022 definitions (change of >10% relative to the predicted value for FEV1 or FVC). Data were collected by CUH on their Electronic Patient Record Research and Innovation (ERIN) database and analysed retrospectively by the researchers.
Nearly half of the patients had a history of smoking, and 58 per cent of the patients were referred for asthma or suspected asthma, while the remaining patients were referred for other conditions.
A quarter of the patients met the ATS/ERS 2005 BDR definition, and 26 per cent met the ATS/ERS 2022 BDR definition. A higher proportion of patients showed a positive BDR when tested in the morning compared to the afternoon (28 per cent vs. 22 per cent, respectively, for ATS/ERS 2005 and 28 per cent vs. 23 per cent for the ATS/ERS 2022).
The researchers found that starting at 8.30am, with every hour that passed during the working day, the chances of a positive response to the test decreased by 8 per cent.
Dr Ben Knox-Brown, lead research respiratory physiologist at Royal Papworth Hospital NHS Foundation Trust, said: ‘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.’
He added: ‘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.’
The researchers also discovered that individuals tested in autumn were 33 per cent less likely to have a positive result than those tested in winter.
Dr Akhilesh Jha, a clinician scientist at the University of Cambridge and Honorary Consultant at CUH, said there may be a combination of factors behind this difference. ‘Our bodies have natural rhythms – our body clocks. Throughout the day, the levels of different hormones in our bodies go up and down, and our immune systems perform differently. Any of these factors might affect how people respond to the lung function test.’
Increasing evidence shows that the time a patient is treated can affect treatment outcomes. For example, people respond to vaccines differently depending on the time of day they are administered. The researchers say this study’s findings should be considered when interpreting the tests commonly performed to diagnose asthma.
