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How is asthma diagnosed?

Asthma can be diagnosed in your doctor's office based on your symptoms. However, other studies, such as lung function tests, exhaled nitric oxide, allergy testing and chest x-rays may help in making the diagnosis.

To diagnose asthma in children doctors perform the following breathing tests:

  • spirometry
  • peak flow measures
  • formal lung function testing

Doctors would also perform an exam, and consider symptoms such as coughing, wheezing, shortness of breath and chest tightness and what provokes these symptoms.

Your health care provider will ask about your medical history including whether any of your family members have asthma and if you smoke, have allergies or are exposed to pollutants. During a physical exam, your health care provider will ask you to breathe normally into a mouthpiece attached to a machine called a spirometer. A spirometer measures the amount and speed at which you breathe air in and out of your lungs. You may also be asked to use a peak flow meter during the office visit as well as later to monitor your symptoms at home. This device measures how well you can breathe out air from your lungs. Your health care provider also may use blood tests, allergy tests and sinus or chest X-rays to aid in the diagnosis.

Dr. Mehmet Oz, MD
Cardiologist (Heart Specialist)

If you truly have asthma, we can diagnose it via pulmonary function tests, or PFTs. Some pediatricians perform these right in their offices, while others send you to a pulmonologist, or lung specialist. During a PFT, you breathe out as hard as you can through a tube, kind of like blowing out a lot of birthday candles at once.

If you have asthma, you don’t breathe as effectively, even with your best effort. If your doctor performs a test called a methacholine challenge, he will have you breathe in a medicine that will make your airways twitchy (that’s the methacholine) and then blow through the tube. Immediately afterward, he’ll administer a medicine that will relieve the twitchiness if you have asthma, causing a great improvement in your PFT. If this test is positive, it means you’ve got asthma.

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To establish a diagnosis of asthma, healthcare providers should determine the following:

  • Episodic symptoms of airflow obstruction or airway hyper-responsiveness are present
  • Airflow obstruction is at least partially reversible
  • Alternative diagnoses are excluded (e.g., vocal cord dysfunction, cough-variant forms of asthma, physiologic dyspnea and protracted or persistent bacterial bronchitis)

In young children and infants, particularly “happy wheezers” or children with primarily “noisy breathing,” also consider etiologies such as laryngomalacia, tracheobronchomalacia, structural airway disease and congenital abnormalities. Common comorbidities include obstructive sleep apnea, allergic bronchopulmonary aspergillosis and gastroesophageal reflux, which should be aggressively treated and evaluated.

In addition to a detailed history and physical exam, accurate and reliable pulmonary function testing (spirometry) is crucial to establishing a diagnosis of asthma and excluding alternative diagnoses. Spirometry before and after inhalation of a short-acting bronchodilator should be performed in patients 5 years old for whom an asthma diagnosis is being considered. Spirometric indices most often used to evaluate obstructive lung disease and asthma are the forced expiratory volume in the first second (FEV1) of forced exhalation expressed as either a percent of the predicted value or as a percent of the forced vital capacity (FVC), an FEV1-to-FVC ratio.

The contents of this website are for informational purposes only and are not intended to be a substitute for professional medical advice, diagnosis, or treatment. Nor does the contents of this website constitute the establishment of a physician patient or therapeutic relationship. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition.

Intermountain Registered Dietitians
Nutrition & Dietetics Specialist

Here’s what your doctor may do to gather information before an asthma diagnosis:

  • During the medical history, your doctor will ask questions about your symptoms and what seems to trigger them. Your doctor will pay particular attention to repeated symptoms. Try to provide as many details as possible, even if they seem unrelated.
  • During your physical examination, your doctor may listen to your breathing and heartbeat, and check your body for signs of allergies. (Allergies are common asthma triggers.)
  • A lung function test (also called a pulmonary function test, or PFT), shows how well your lungs are working. For example, spirometry measures how much air you can breathe out and how fast. In addition to other readings, spirometry can give your forced expiratory volume, or FEV1. FEV1 is the volume of air you can blow out in one second—and it is a useful measure both for diagnosing asthma and for checking asthma control later on. Note that for young children—who often aren’t able to perform lung tests correctly—doctors often rely on a medical history and physical exam to diagnose asthma.
  • With various other tests, your doctor may gather more information about your lungs, your breathing and your asthma triggers. For example, chest x-rays can help rule out other lung problems that could be causing your symptoms. Blood tests and skin prick tests can check for allergies that might cause your asthma symptoms.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.