How Is Asthma Diagnosed?

Male nurse explaining inhaler to boy
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Asthma is a chronic lung disease, leading to recurrent episodes of wheezing (a high-pitched squeaking sound occurring during breathing in and out), a sensation of chest tightness or heaviness, a sense of not getting enough air (shortness of breath), and coughing. In people with asthma, lung airways become inflamed, leading to narrowing of the airways. The muscles around the airways become more sensitive and contract in response to various triggers, causing the symptoms of asthma to occur.

What Causes Asthma to Get Worse?

There are a number of different triggers that can worsen asthma symptoms. These may include exercise, respiratory tract infections (especially the common cold), inhaled allergens (such as pollens, mold spores, pet dander, and dust mites), irritants (such as tobacco smoke), strong emotions, stress or even changes in hormone levels (as with a woman’s menstrual cycle).

How Is Asthma Diagnosed?

While the symptoms of asthma are certainly suggestive of a diagnosis of asthma, particularly if these symptoms get better with the use of inhaled bronchodilators (such as albuterol), simply having symptoms of asthma isn’t enough to make the diagnosis of asthma.

The diagnosis of asthma is dependent on the measurement of reversible airflow obstruction on spirometry. If a particular measurement of lung function, called the FEV1 (forced expiratory volume in 1 second), increases at least 12% and 200 milliliters after the inhalation of a bronchodilator, then a diagnosis of asthma can be made. The FEV1 is how much air can be blown out of the lungs in the first second of exhalation. If this value increases after the inhalation of a bronchodilator, then this means that the bronchodilator was able to relax the muscles in the airway enough to allow more air to come out faster, suggesting the presence of airflow obstruction. Another way to think of this is kinking a garden hose: If a garden hose is kinked, water can still come out. Once the hose becomes unkinked, the water comes out much faster. This is a similar process of how air comes out of the lungs faster when airflow obstruction is resolved with the inhalation of a bronchodilator.

The diagnosis of asthma can also be made through bronchoprovocation, which is a test that decreases lung function on spirometry. People with asthma have increased irritability of the airways in the lungs, and this can lead to a drop in the FEV1 through bronchoprovocation. Bronchoprovocation can be performed using the inhalation of medications that cause direct contraction of the muscles in the airway (such as with methacholine), release of allergic chemicals from mast cells in the lungs (such as with mannitol or allergens), or with exercise or inhaled cold air. A positive challenge, which is usually defined as a decrease in the FEV1 of 15-20% (depending on the test being used), is suggestive of (but not diagnostic) asthma because a positive bronchoprovocation test can also occur in people with allergic rhinitis and recent respiratory tract infection. Negative bronchoprovocation tests can be very useful at excluding the possibility of asthma.

Other tests that can suggest or refute the presence of asthma include peak flow measurements, inflammatory biomarkers such as exhaled nitric oxide and sputum eosinophils. None of these tests are considered diagnostic for asthma at the present time, although may be helpful at monitoring asthma in people already diagnosed with spirometry.

Therefore, asthma should ONLY ever be diagnosed with the use of spirometry — either using a bronchodilator to increase FEV1 or by using various bronchoprovocation testing to decrease FEV1.


DISCLAIMER: The information contained in this site is for educational purposes only, and should not be used as a substitute for personal care by a licensed physician. Please see your physician for diagnosis and treatment of any concerning symptoms or medical condition.

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