Despite What We May Think, Diagnosing Asthma Isn't Easy

Aaron B. Holley, MD


November 29, 2018

Diagnosing asthma isn't easy? Really? Isn't it well described and extensively researched? Aren't there multiple national- and international-level organizations that publish comprehensive guidelines? Don't we have an array of objective tests to confirm (or exclude) the diagnosis?

The answer to all these questions is "yes." However, as is often the case, with increased knowledge the reality grows more complicated.

In a recently published clinical review paper, researchers from Canada summarized the literature on under- and overdiagnosis of asthma.[1] The authors have conducted and published important research on this subject, making them well qualified to lead this discussion. Their findings are sobering, and improving performance won't be easy.

The authors start by acknowledging that asthma is common. They cite prevalence estimates of 0.2%-21.0% in adults worldwide,[2,3] with approximately 300 million individuals affected globally.[4] They noted prevalence rates of 20%-73% and 30%-60% for underdiagnosis and overdiagnosis, respectively. Even the low ends of these ranges are disturbingly high.

So why are patients underdiagnosed? The authors cite three general causes: patient factors (underreporting, poor perception); underdiagnosis by general practitioners; and poor sensitivity of spirometry.

As for overdiagnosis, causes include failure to obtain objective lung testing (to confirm the presence of asthma and rule out the plethora of asthma mimickers) and remission of symptoms over time.[1]

The authors propose public education, specific management algorithms (borrowed from the Global Initiative for Asthma [GINA] report[3] and some of their previous work[5]), and objective lung testing as methods to improve our performance.

Their suggestions are reasonable enough, but challenges remain.

The GINA report defines asthma as "a history of respiratory symptoms such as wheeze, shortness of breath, chest tightness, and cough that vary over time and in intensity, together with variable expiratory airflow limitation."[3] Cough and dyspnea are common complaints,[6,7] and neither is specific for asthma. Spirometry is not sensitive for detecting asthma, and advanced testing (eg, bronchoprovocation [BP], fractional exhaled of nitric oxide) is not readily available. Indirect BP tests, which add to the sensitivity of methacholine challenge testing,[8] are even harder to obtain, particularly in the United States.

Statistical and Clinical Realities

Cough and dyspnea are common, and asthma has a high prevalence. Clinicians are right to have asthma at the top of their differential diagnosis, but most cough and dyspnea will not be due to asthma. Confirmatory testing takes time and effort and is not readily available. The proliferation of knowledge on asthma phenotypes simply complicates matters. Asthma is a very heterogeneous disease with variable presentation.[9,10,11]

This review[1] on under- and overdiagnosis is excellent. Clinicians would be advised to read it carefully, study the algorithms, and refer to a specialist when their patient is not responding to standard therapies. Above all else, don't oversimplify. Diagnosing asthma isn't as easy as it might seem.

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