A groundbreaking study by researchers at the University of Cambridge and Royal Papworth Hospital NHS Foundation Trust (RPH) discovered that lung function tests used to detect asthma are much more reliable when performed in the morning. The study, which used data from 1,600 individuals, also discovered significant seasonal differences, with test results changing between autumn and winter.

Asthma, a common respiratory disorder that affects around 6.5% of people over the age of six in the United Kingdom, can produce symptoms such as wheezing and difficulty breathing. Inhalers and nebulisers can help free up the airways. While asthma attacks are known to be more common at night or early in the morning, researchers wanted to discover if circadian rhythms—our internal body clocks—also affect the efficiency of diagnostic lung function testing.

The study, which took place at the Victor Phillip Dahdaleh Heart and Lung Research Institute, focused on spirometry, a common test used to examine lung function. The test requires the patient to take a deep breath and aggressively exhale into a tube. Patients then receive a dosage of salbutamol, a bronchodilator that widens the airways, before repeating the test. A significant improvement in lung function indicates the presence of asthma.

Using the Electronic Patient Record Research and Innovation (ERIN) database, which gives safe access to real-world patient data, the researchers examined cases from Cambridge University Hospitals NHS Foundation Trust (CUH) from 2016 to 2023. After controlling for characteristics such as age, gender, body mass index (BMI), smoking history, and starting lung function impairment, a clear pattern emerged: the spirometry test's reliability decreases as the day passes.

The findings, published in Thorax, show that beginning at 8:30 a.m., the likelihood of a positive response to the test—indicating airway blockage and possible asthma—decreases by about 8% every hour throughout the workday.

Dr. Ben Knox-Brown, Lead Research Respiratory Physiologist at RPH, highlighted the significance of the findings: "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 we were surprised by the size of the effect." This has significant ramifications. Doing the test in the morning provides a more reliable picture of a patient's response to medicine than doing it in the afternoon, which is crucial when verifying a diagnosis like asthma."

Beyond time-of-day impacts, the study discovered seasonal differences. Patients examined in the autumn were 33% less likely to show a favourable response than those tested in the winter.

Dr. Akhilesh Jha, a Medical Research Council Clinician Scientist at the University of Cambridge and Honorary Consultant in Respiratory Medicine at CUH, suggested that these changes could be attributed to our bodies' intrinsic cycles, or clocks. Throughout the day, the amounts of various hormones in our bodies fluctuate, and our immune systems function differently, for example. These factors may impact how individuals respond to lung function tests. We're seeing more evidence that the time of day or season influences our health and how we respond to therapies. We know that people react differently to immunisations depending on whether they are given in the morning or in the afternoon. Our study's findings corroborate this hypothesis and may need to be considered when interpreting the outcomes of these regularly administered tests."

This study emphasises our expanding understanding of how circadian rhythms and seasonal variables affect medical diagnosis and treatment responses. Moving forward, healthcare professionals may need to consider time-of-day differences when scheduling lung function tests in order to improve diagnostic accuracy and patient results.