The classic signs and symptoms of asthma are shortness of breath, cough (often worse at night), and wheezing (high-pitched whistling sound produced by turbulent airflow through narrow airways, typically with exhalation). Many patients also report chest tightness. It is important to note that these symptoms are episodic, and individuals with asthma can go long periods without any symptoms.
Common triggers for asthmatic symptoms include exposure to allergens (pets, dust mites, cockroach, molds, and pollens), exercise, and viral infections. Other triggers include strong emotion, odor exposure, and temperature extremes. Tobacco use or exposure to secondhand smoke complicates asthma management.
Many of the symptoms and signs of asthma are nonspecific and can be seen in other conditions as well. Symptoms that might suggest conditions other than asthma include new symptom onset in older age, the presence of associated symptoms (such as chest discomfort, lightheadedness, palpitations, and fatigue), and lack of response to appropriate medications for asthma.
The physical exam in asthma is often completely normal. Occasionally, wheezing is present. In an asthma exacerbation, the respiratory rate increases, the heart rate increases, and the work of respiration increases. Individuals often require accessory muscles to breathe, and breath sounds can be diminished. It is important to note that the blood oxygen level typically remains fairly normal even in the midst of a significant asthma exacerbation. Low blood oxygen level is therefore concerning for impending respiratory failure. IMAGESAsthmaSee a medical illustration of the bronchioles plus our entire medical gallery of human anatomy and physiologySee Images
How do doctors diagnose asthma?
The diagnosis of asthma begins with a detailed history and physical examination. Primary-care providers are familiar with the diagnosis of asthma, but specialists such as allergists or pulmonologists may be involved. A typical history is an individual with a family history of allergic conditions or a personal history of allergic rhinitis who experiences coughing, wheezing, and difficulty breathing, especially with exercise, viral infections, or during the night. In addition to a typical history, improvement with a trial of appropriate medications is very suggestive of asthma.
In addition to the history and exam, the following are diagnostic procedures that can be used to help with the diagnosis of asthma:
- Lung function testing with spirometry: This test measures lung function as the patient breathes into a tube. If lung function improves significantly following the administration of a bronchodilator, such as albuterol, this essentially confirms the diagnosis of asthma. It is important to note, however, that normal lung function testing does not rule out the possibility of asthma.
- Measurement of exhaled nitric oxide (FeNO): This can be performed by a quick and relatively simple breathing maneuver, similar to spirometry. Elevated levels of exhaled nitric oxide are suggestive of T2 inflammation seen in some types of asthma.
- Skin testing for common aeroallergens: The presence of sensitivities to environmental allergies increases the likelihood of asthma. Of note, skin testing is more accurate than blood work (in vitro testing) for environmental allergies. Testing for food allergies is not indicated in the diagnosis of asthma.
- Doctors often perform blood tests for the allergic antibody (IgE) and eosinophils to establish the present of T2 high asthma.
- Other potential but less commonly used tests include provocation testing such as a methacholine challenge, which tests for airway hyperresponsiveness. Hyperresponsiveness is the tendency of the breathing tubes to constrict or narrow in response to irritants. A negative methacholine challenge makes asthma unlikely. Specialists sometimes also measure sputum eosinophils, another marker for “allergic” inflammation seen in asthma. Chest X-rays or CT-scans may show hyperinflation, but are often normal in asthma. Tests to rule out other conditions, such as cardiac testing, may also be indicated in certain cases.