Routine asthma test is more reliable in the morning and affected by seasons, Cambridge researchers find

A lung function test that is used to help diagnose asthma is more effective in the morning and becomes less reliable throughout the day, researchers have found.

Its reliability also differs significantly in winter compared to autumn, they discovered used real world data from 1,600 patients.

About 6.5 per cent of people over the age of six in the UK have the lung condition, which can cause wheezing and shortness of breath. The majority of asthma attacks occur at night or early in the morning.

This might be due to cooler nighttime air and exposure to dust mites and allergens, but also suggests our body clocks 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), explored whether these ‘circadian rhythms’ also impact diagnosis.

Spirometry tests involve taking a deep breath in, then breathing out hard and fast for as long as possible into a tube to assess lung function.

An individual being tested is then administered the drug salbutamol via an inhaler or nebuliser, before retaking the spirometry test.

Since salbutamol opens up the airways, a positive test result – meaning one showing a difference in the two readings - indicates the airways were narrower or obstructed to begin with, suggesting asthma.

Cambridge University Hospitals’ Electronic Patient Record Research and Innovation (ERIN) database enables researchers to access patient data securely.

It allowed University of Cambridge researchers to analyse 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.

They 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, 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.”

Individuals were also 33 per cent less likely to have a positive result if tested in autumn compared to those tested during winter.

Dr Akhilesh Jha, a Medical Research Council clinician scientist at Cambridge and honorary consultant in respiratory medicine at CUH, said: “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, 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.”