Routine asthma test more reliable in morning and has seasonal effects, say doctors

A lung function test used to help diagnose asthma works better in the morning, becoming less reliable throughout the day, Cambridge researchers have found.

Using real world data from 1,600 patients, available through a database created for speeding up research and innovation, the team also found that its reliability differs significantly in winter compared to autumn.

Asthma is a common lung condition that can cause wheezing and shortness of breath, occasionally severe. Around 6.5% of people over six years old in the UK are affected by the condition. Treatments include the use of inhalers or nebulisers to carry medication into the lungs.

The majority of asthma attacks occur at nighttime or early in the morning. Although this may in part be due to cooler nighttime air and exposure to dust mites and allergens, it also suggests that circadian rhythms – our ‘body clocks’ – likely play a role.

Researchers at the Victor Phillip Dahdaleh Heart and Lung Research Institute, a collaboration between the University of Cambridge and Royal Papworth Hospital NHS Foundation Trust (RPH), wanted to explore whether these circadian rhythms may also have an impact on our ability to diagnose asthma, using routinely performed clinical testing.

Typically, people with suspected asthma will be offered a spirometry test, which involves taking a deep breath in, then breathing out hard and fast for as long as possible into a tube to assess lung function. They will then be administered the drug salbutamol via an inhaler or nebuliser, and shortly afterwards retake the spirometry test.

Salbutamol works by opening up the airways, so a positive test result – that is, a difference in readings between the initial and follow-up spirometry tests – means that the airways must have been narrower or obstructed to begin with, suggesting that the patient could have asthma.

Cambridge University Hospitals NHS Foundation Trust (CUH) has recently set up the Electronic Patient Record Research and Innovation (ERIN) database so that researchers can access patient data in a secure environment to help in their research and speed up improvements in patient care.

Using this resource, the Cambridge team analysed data from 1,600 patients referred to CUH between 2016 and 2023, adjusted for factors such as age, sex, body mass index (BMI), smoking history, and the severity of the initial impairment in lung function.

In findings published today in Thorax, 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 – in other words, the patient’s lungs responding to treatment, suggesting that they could have asthma – decreased by 8%.

Dr Ben Knox-Brown, Lead Research Respiratory Physiologist at RPH, 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.

“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 were 33% less likely to have a positive result if tested during autumn when compared to those tested during winter.

Dr Akhilesh Jha, a Medical Research Council Clinician Scientist at the University of Cambridge and Honorary Consultant in Respiratory Medicine at CUH, said that there may be a combination of factors behind this difference.

“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.

“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.”

Reference:

Knox-Brown B, Kon FC, Sylvester KP, et alEffect of time of day and seasonal variation on bronchodilator responsiveness: the SPIRO-TIMETRY studyThorax Published Online First: 11 March 2025. doi: 10.1136/thorax-2024-222773