You’re walking outside when suddenly, your throat deflates and your breathing becomes strained. You hear that all too familiar wheezing sound, and you know that your pleasant afternoon stroll has been hijacked by a severe asthma attack. For the 10% of people diagnosed with asthma, a disease that causes chronic airway inflammation, this experience is almost routine. While many asthma patients can manage their symptoms with an inhaler, those that are misdiagnosed with asthma cannot, emphasizing the importance of accurate diagnostic methods.

How is asthma diagnosed?

If asthma is suspected based on a patient’s medical history, initial tests are often conducted using peak flow or spirometry. Peak flow testing is done with a simple handheld device that patients quickly and forcefully exhale into. After multiple attempts, the highest rate of exhalation is recorded as the patient’s maximum peak expiratory flow rate (PEFR) and is compared to later measurements taken during a suspected asthma attack. Results that are less than 80% of a patient’s PEFR are used as an initial indicator of asthma. Spirometry is a similar but more complex testing method that studies both the patient’s inhalation and exhalation patterns. Multiple tests, including forceful exhalation, steady exhalation, and forceful inhalation are employed to measure lung capacity and airway obstruction. Spirometric results that reflect unusually low air flow or lung capacity are used to identify asthma.

After the initial peak flow or spirometry testing, a bronchodilator or challenge test is given to confirm the asthma diagnosis. Both of these tests are conducted by measuring peak flow or spirometry before and after a specific chemical is administered to the patient. Since asthma is defined by its reversibility, or in other words, its ability to be intermittently triggered, challenge testing is considered the gold standard of asthma tests. Challenge testing involves directly provoking an asthma response by inhaling an irritant such as histamine or methacholine. A decline in spirometry or peak flow readings would confirm the asthma diagnosis. On the other hand, bronchodilator testing is performed by inhaling a drug that relaxes the airways and restores their full function. In this case, an improvement in peak flow or spirometry results would support an asthma diagnosis.

What could be misdiagnosed as asthma?

Despite these extensive testing methods, research has shown that up to 33% of asthma diagnoses are incorrect, causing patients who may have other conditions to believe they have asthma instead. Dozens of asthma-like conditions have been identified, ranging from relatively minor disorders like seasonal allergies to severe respiratory diseases like chronic obstructive pulmonary disorder (COPD). Furthermore, misdiagnosis could also occur if true asthma is falsely diagnosed as one of its mimicking diseases.

These misdiagnoses tend to be caused by a lack of sensitivity or specificity in currently available testing methods. If a patient does not exhibit asthma symptoms during their peak flow or spirometry test, the relatively low sensitivity of these tests may not be sufficient to recognize their underlying asthma. Additionally, the limited specificity of these tests could allow a patient with an asthma-like disease to have results similar to a true asthma patient, confounding their diagnosis. Misdiagnosis also affects healthy asymptomatic individuals, since the substances used in bronchodilator and challenge tests are not asthma-specific and can affect the general population.

What are the consequences?

Notably, many conditions that mimic asthma symptoms have vastly different treatment patterns than asthma. Oral corticosteroid tablets used for management of severe asthma can have wide-ranging negative health impacts if incorrectly prescribed, and treatments for asthma-like lung conditions may be ineffective at treating asthma itself. Since the underlying condition is not being targeted, its symptoms will continue to affect the patient’s general quality of life. Over time, untreated asthma or asthma-like diseases can also worsen, resulting in hospitalization, long-term lung deterioration, or death.

With such a high prevalence of asthma misdiagnosis, it is clear that we as a society need better testing methods for diagnosing asthma and its analogues. Although asthma currently cannot be cured, it is one of the few diseases whose symptoms can be thoroughly and effectively treated with minimal side effects. As such, more accurate diagnosis would be a giant step towards improving the lives of millions worldwide.