New research from the University of Cambridge and Royal Papworth Hospital NHS Foundation Trust reveals that the timing of asthma diagnostic tests significantly impacts their reliability, with morning tests providing more accurate results than those conducted later in the day.
The study, published in the journal Thorax, analyzed data from 1,600 patients who underwent standard spirometry testing between 2016 and 2023. Researchers discovered that starting at 8:30 AM, the likelihood of detecting a positive response to salbutamol—indicating potential asthma—decreased by 8% with each passing hour during the working day.
"We expected to find a difference in how people responded to the lung function test based on time of day, but even so, we were surprised by the size of the effect," said Dr. Ben Knox-Brown, Lead Research Respiratory Physiologist at Royal Papworth Hospital and lead investigator of the study.
Circadian Rhythms Impact Diagnostic Accuracy
The findings align with established knowledge that most asthma attacks occur at night or early morning, suggesting circadian rhythms play a crucial role in the condition's manifestation and diagnosis.
Standard asthma testing involves a two-step spirometry process. Patients first perform a baseline lung function test, followed by administration of salbutamol—a bronchodilator that opens airways—before repeating the test. A significant improvement in the second test suggests the airways were initially obstructed, potentially indicating asthma.
Dr. Akhilesh Jha, a Medical Research Council Clinician Scientist at the University of Cambridge and Honorary Consultant in Respiratory Medicine, explained: "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."
Seasonal Variations in Test Reliability
Perhaps even more surprising was the discovery of significant seasonal variations in test results. Patients were 33% less likely to show a positive response to salbutamol when tested during autumn compared to winter.
The research team utilized the Electronic Patient Record Research and Innovation (ERIN) database at Cambridge University Hospitals NHS Foundation Trust, which allowed them to analyze real-world patient data in a secure environment. Their analysis adjusted for factors including age, sex, body mass index, smoking history, and initial lung function impairment.
Clinical Implications for Asthma Management
These findings have important implications for asthma diagnosis and management. "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," Dr. Knox-Brown emphasized.
The research adds to growing evidence that time-of-day factors significantly impact medical testing and treatment efficacy across various conditions. "We know, for example, that people respond differently to vaccinations depending on whether they're administered in the morning or afternoon," noted Dr. Jha. "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."
Asthma Burden and Current Diagnostic Challenges
Asthma affects approximately 6.5% of people over six years old in the UK. The condition causes wheezing, shortness of breath, and occasionally severe attacks that can be life-threatening. Current treatments primarily involve inhalers or nebulizers to deliver medication directly to the lungs.
Accurate diagnosis remains crucial for effective management, and this study suggests that clinical guidelines may need to consider time-of-day and seasonal factors when scheduling diagnostic tests for suspected asthma patients.
Future Research Directions
While this study provides compelling evidence for the impact of timing on asthma test reliability, further research is needed to understand the precise biological mechanisms behind these variations. Additional studies might explore whether similar time-of-day and seasonal effects influence the efficacy of asthma treatments themselves, potentially leading to more personalized treatment schedules.
The research team suggests that healthcare providers should consider scheduling spirometry tests in the morning when possible, particularly for patients with borderline or inconclusive previous results. They also recommend that clinicians take seasonal factors into account when interpreting test results, especially for tests conducted during autumn months.
This study represents an important step toward more precise and personalized approaches to asthma diagnosis and management, highlighting how seemingly minor factors like appointment timing can significantly impact diagnostic accuracy and, ultimately, patient care.
