Mayo Clinic Health Library

Asthma: Steps in testing and diagnosis

Updated: 06-23-2011

Asthma diagnosis is based on a number of things, including a physical exam, answers to questions about your symptoms and overall health, and results of lung tests or other tests.

Medical history

The first step in diagnosing asthma is talking to your doctor about your symptoms and your health. This can provide clues as to whether your symptoms are most likely caused by asthma or may be caused by something else. Your doctor will likely ask:

  • What are your exact symptoms? When do they occur, and does anything specific seem to trigger them?
  • Are you often exposed to tobacco smoke, chemical fumes, dust or other airborne irritants?
  • Do you have hay fever or another allergic condition?
  • Do you have any blood relatives with asthma, hay fever, or other allergies?
  • What health problems do you have?
  • What medications or herbal supplements do you take? (Many medications can trigger asthma.)
  • What is your occupation?
  • Do you have pet birds or raise pigeons? (In some people, exposure to birds can cause asthma-like symptoms.)

Physical exam

Your doctor may:

  • Examine your nose, throat and upper airways (upper respiratory tract).
  • Use a stethoscope to listen to your breathing. Wheezing — high-pitched whistling sounds when you breathe out — is one of the main signs of asthma.
  • Examine your skin for signs of allergic conditions such as eczema and hives.

Your doctor will want to know whether you have common signs and symptoms of asthma, such as:

  • Recurrent wheezing
  • Coughing
  • Trouble breathing
  • Chest tightness
  • Symptoms that occur or worsen at night
  • Symptoms that are triggered by cold air, exercise or exposure to allergens.

Asthma signs and symptoms in children
In children, additional signs and symptoms may signal asthma. These may include:

  • Breathing that is louder than normal or faster than normal. Newborns typically take 30 to 60 breaths a minute. Toddlers typically take 20 to 40 breaths a minute.
  • Frequent coughing or coughing that worsens after active play.
  • Coughing, clear mucus and a runny nose caused by hay fever.
  • Frequent missed school days.
  • Limited participation in physical activities.

Lung tests

Lung tests (pulmonary function tests) such as spirometry are often used to help confirm an asthma diagnosis. These tests check how well your lungs are working. During spirometry, you take a deep breath and forcefully breathe out (exhale) into a tube connected to a machine called a spirometer. This records both the amount (volume) of air you breathe out and how quickly you can exhale. If certain key measurements are below normal for a person your age, it may be a sign that your airways are narrowed by asthma.

After taking lung test measurements, your doctor may ask you to inhale an asthma drug to open air passages. Then, you'll do the lung tests again. If your measurements improve significantly after taking the medication, you may have asthma.

Challenge test
With this test, your doctor tries to trigger asthma symptoms by having you inhale a substance that causes the airways to narrow in people with asthma, such as methacholine (meth-uh-KO-leen).

If you appear to have asthma triggered by exercise (exercise-induced asthma), you may be asked to do physical activity to see whether it triggers symptoms.

After taking action to trigger your symptoms, you'll retake the spirometry test. If your spirometry measurements are normal, you probably don't have asthma. But if your measurements have fallen significantly, it's possible you do.

Lung tests in children
Doctors seldom do lung tests in children under age 5. Instead, diagnosis is generally based on a child's signs and symptoms, medical history, and physical examination. It can be especially difficult to diagnose asthma in young children because there are many conditions that cause asthma-like symptoms in this age group.

If your child's doctor suspects asthma, the doctor may prescribe a bronchodilator — a drug that opens the airways. If your child's signs and symptoms improve after using the bronchodilator, your child may have asthma.

Exhaled nitric oxide test
With this test, you breathe into a tube connected to a machine that measures the amount of nitric oxide gas in your breath. Nitric oxide gas is produced by the body normally, but high levels in your breath can mean your airways are inflamed — a sign of asthma.

Additional tests: Ruling out conditions other than asthma

Depending on your age, your medical history and initial testing, your doctor may suspect that you have a condition other than asthma. Conditions that can cause asthma-like symptoms include:

  • Something blocking in the airways (airway obstruction). Breathing a piece of food or a small object into the airways is especially common in infants and young children.
  • Another lung disease such as emphysema or chronic obstructive pulmonary disease (COPD).
  • A tumor or tumors in the airways.
  • Bronchiolitis (BRONG-ke-oh-LIE-tis). This type of airway inflammation often stems from a viral lung infection such as respiratory syncytial (sin-SISH-ul) virus, particularly in children under 2.
  • Lung infection (pneumonia) caused by a bacteria or virus.
  • A blood clot in the lung (pulmonary embolism).
  • Heart failure (congestive heart failure).
  • Vocal cord dysfunction, which is also called paradoxical vocal cord movement or laryngeal dysfunction.

To rule out possible causes of your breathing problems, you may need tests such as:

  • Chest and sinus X-rays
  • Blood tests — for example, a complete blood count (CBC) test
  • Computerized tomography (CT) scans of the lungs
  • Gastroesophageal reflux assessment
  • Examination of the phlegm in your lungs (sputum induction and examination) for signs of a viral or bacterial infection.

Your doctor may also want to see whether you have any other conditions that often accompany asthma and can make symptoms worse. These include:

  • Heartburn (gastroesophageal reflux disease, or GERD)
  • Hay fever
  • Sinusitis

Your doctor may also perform allergy tests. These can be either skin tests or blood tests, or both. Allergy tests aren't specifically used to diagnose asthma. But, they can help identify an allergic condition, such as hay fever, that may be causing your symptoms or worsening existing asthma.

For some people, asthma diagnosis is straightforward. But for others, diagnosing the cause of breathing problems is a challenge. It can be difficult to differentiate asthma from other conditions — particularly in young children. When existing asthma is worsened by another condition, such as hay fever, it can further complicate diagnosis. Your doctor will need to piece together all of the information possible to determine what's causing your symptoms. Even if a diagnosis isn't certain, your doctor may prescribe medications or other treatment to see whether it helps.

Because numerous conditions can cause asthma-like symptoms, it may take some time — and patience — to get the correct diagnosis and determine the best course of treatment.

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