Photo Credit: Vasyl Faievych

Clinicians should account for the time of day when performing asthma diagnostic tests, as most patients experience more symptoms overnight and in the morning.

Fractional exhaled nitric oxide (FeNO) and bronchodilator reversibility tests performed in the morning are more likely to yield positive results than afternoon tests, according to a study published in EJR Open Research.

“As asthma is such a common and frequently misdiagnosed disease, these findings suggest a significant impact of timing on clinical decision making, particularly in those with borderline results,” wrote Ran Wang, MRes, and colleagues from the University of Manchester and Manchester University FHS Foundation Trust, Manchester, England.

The study investigated the impact time of day had on results of key diagnostic tests for asthma. The researchers included 140 symptomatic, untreated patients with suspected asthma who underwent spirometry and bronchodilator reversibility, FeNO, and methacholine and mannitol bronchial challenge tests. Patients also had blood eosinophils measured. Appointment time was based on patient preference and clinic availability between 09:00 and 17:00.

Among participants with definitive outcomes, 59.3% had asthma. 84% of those with asthma and 68% of those without asthma reported same-day variation in symptoms. According to the study, symptoms were worse overnight and in the morning for the majority. In contrast, symptoms were at their lowest levels between 09:00 and 17:00.

As the day progressed, the prevalence of positive bronchodilator reversibility tests in diagnostic settings dropped, the study found, from 31.3% before 11:00 to 14.8% after 15:00. After adjustment for baseline airflow obstruction, the likelihood of positive bronchodilator reversibility in the afternoon did not significantly differ from in the morning.

The effect of timing on median FeNO levels was pronounced in atopic patients, with a fall of 6.2 parts per billion per hour as the day progressed. Similar to bronchodilator reversibility testing, the proportion of positive FeNO tests fell as the day went on. Analysis found that FeNO testing performed in the morning was more likely positive than in the afternoon.

“Importantly, FeNO has recently been recommended by the American Thoracic Society to monitor asthma treatment; we would advocate that the time of day is taken into account to improve the usefulness of FeNO in this setting,” the researchers wrote.

“As self-reported time-of-day symptom patterns coincide with airflow obstruction in patients with asthma, it is plausible that assessing the airflow obstruction and associated inflammation at the time of day when patients are most symptomatic may improve diagnostic efficiency.”