Asthma is a chronic disease involving inflammation of the airways in the lungs, making breathing difficult. It has multiple causes and can be treated, but not cured. In the past, asthma was often underdiagnosed, but in recent years, there has been increased attention on the need for timely treatment.
That awareness has led to heightened vigilance on the part of physicians, as well as a rise in reported cases. According to the U.S. Centers for Disease Control and Prevention, 18.4 million American adults currently suffer from asthma. Yet an emerging body of research has found that some people diagnosed with asthma do not actually have the illness-because either they were misdiagnosed in the first place or they have undergone spontaneous remission without knowing it. In some cases, people misdiagnosed with asthma might actually be suffering from another serious ailment.
These findings have prompted health officials to reinforce the message that any asthma diagnosis should be confirmed with an objective test, such as spirometry. Moreover, such testing should be part of ongoing disease management, to ensure that people being treated for asthma still have the condition.
Why is asthma sometimes hard to diagnose?
The main symptoms of asthma, which include shortness of breath, wheezing, coughing, and production of phlegm, are common in many respiratory ailments and other conditions. As a result, a person with a persistent dry cough, for example, may be suspected of having asthma when in actuality that person has gastroesophageal reflux disease (GERD). At the same time, people with asthma are much more likely than those without it to suffer from GERD, and there is some reason to believe that each illness can exacerbate the other.
Other conditions that can make asthma worse or that might be misdiagnosed as asthma include obstructive sleep apnea, sinusitis, congestive heart failure, and allergic bronchopulmonary aspergillosis (a lung disease that occurs in some people who are allergic to a type of fungus called Aspergillus). Certain medications, such as ACE inhibitors (used to treat high blood pressure and heart disease), can produce asthma-like respiratory symptoms. ACE inhibitors may also trigger symptoms in some individuals who have asthma. Beta-blockers and nonsteroidal anti-inflammatory drugs (NSAIDs) are also known to exacerbate symptoms in some people with asthma.
Moreover, there are multiple types of asthma, all with different causes and triggers. Often, asthma is associated with allergies-especially allergies to dust mites. In other instances, it is linked to exposure to inhaled fumes, gases, dust, or other potentially harmful substances while on the job. Some people experience exacerbation of symptoms after vigorous exercise.
Confirming a suspected diagnosis of asthma
To obtain an accurate diagnosis of asthma, you must have a pulmonary function test. The most common is a simple breathing test called spirometry, which is often performed in the doctor’s office. This test involves blowing through a tube into an instrument, called a spirometer, to assess lung capacity. Specifically, spirometry assesses how much air you can inhale and exhale, as well as how quickly you exhale. After an initial test, patients receive a bronchodilator (a medication that increases airflow in the lungs) and undergo a second round of spirometry to assess changes in obstructive levels and confirm or rule out a suspected asthma diagnosis.
While a positive spirometry test can result in an asthma diagnosis, a negative result does not necessarily rule it out. Therefore, according to guidelines from the National Asthma Education and Prevention Program (NAEPP), if you have negative or inconclusive spirometry test results but still experience asthma-like symptoms, your doctor should consider further testing.
One commonly used option is the methacholine challenge test (MCT). For this test, you inhale a very low dose of methacholine-a medication that causes airway contractions and spasms in people with asthma. (If your airways do indeed tighten during this test, you will be given an inhaled bronchodilator to open them.)
NAEPP guidelines cite the importance of testing in making an asthma diagnosis. Nonetheless, many doctors identify asthma solely through a medical history and clinical examination, without performing the recommended diagnostic assessments. Studies have shown that in community settings, less than half of asthma diagnoses are confirmed with spirometry. Moreover, because asthma can wane or go into remission, pulmonary function testing should be repeated at regular intervals to ensure that patients are not taking medications for an illness that is largely dormant or no longer present. Testing is also important as a way of ruling out asthma, allowing your doctor to focus on other possible causes of symptoms.
Studies show evidence of overdiagnosis
Several studies have confirmed that more people have an asthma diagnosis than actually have the illness.
- A Canadian study published in 2017 in JAMA (Journal of the American Medical Association) evaluated more than 600 individuals who had received a diagnosis of asthma from a doctor in the previous five years. One-third of those participants were found not to have asthma at the time of evaluation; other researchers have reported similar figures. These findings do not mean that all of the patients who did not have asthma at the time of the researchers’ evaluation were previously misdiagnosed. In some cases, and for unknown reasons, asthma can wane for an extended period.
- A 2015 study in the Journal of Asthma examined 226 patients with suspected asthma who were referred to an allergy clinic for further diagnosis. The patients all had asthma-like symptoms but negative or inconclusive spirometry tests. The investigators found that more than half of those patients did not actually have the disease, according to an MCT. Yet among those in whom asthma was ruled out, more than half (51 percent) had been taking anti-asthma medications.
- In a 2013 study of asthma and obesity in Respiratory Medicine, researchers found evidence of both overdiagnosis and underdiagnosis of asthma. Among 86 obese patients, 32 had received a prior asthma diagnosis from a physician. Of that group, 41 percent were found not to have asthma at the time of the study. Of the 54 patients without a current asthma diagnosis, the condition was detected in about a third.
Why overdiagnosis is an important concern
The issue of overdiagnosis and continued treatment for people whose asthma is in remission is a serious one. Corticosteroids, most often in the form of inhalants, are the most effective means of reducing inflammation and providing relief from asthma symptoms. But long-term use of inhaled corticosteroids, particularly at high doses, can lead to other serious problems; some research has demonstrated an increased risk of cataracts, higher blood glucose levels or type 2 diabetes, and an increased risk of fractures and pneumonia.
What’s more, if you have another condition-for example, congestive heart failure-that is misdiagnosed as asthma, you are not only receiving medication you don’t need, but you are not being treated for your actual illness. In the 2017 JAMA study discussed earlier, 2 percent of the participants who had been misdiagnosed with asthma were found instead to have serious cardiorespiratory conditions for which they were not receiving care.
What if your doctor tells you that it’s asthma?
If your doctor diagnoses you with asthma based solely on a medical history and a clinical examination, be sure to request spirometry or an MCT for confirmation. Even if you received one of these tests for asthma in the past, if your symptoms are under control, you should undergo testing again at least every one to two years; it is possible you are in full or partial remission and might no longer need treatment.