Asthma Tests

Asthma Tests


Physicians use a variety of techniques to determine if a person has asthma, and to manage asthma treatment. These include tests that:

  • Measure how efficiently a patient’s lungs are working. This may include pulmonary function tests and arterial blood gas tests.

  • Identify allergens or other factors that might trigger asthma symptoms. Tests for this purpose may include bronchoprovocation tests and allergy skin tests.

Most asthma tests take place at a medical facility, but some – such as testing with a peak flow meter – can be performed by an individual at home. Experts agree that asthma tests present little or no risk of harm to the patient when done correctly.

The results of asthma tests may lead to a physician prescribing asthma medication and offering other preventative-care advice to individuals diagnosed with asthma. Once a person has been diagnosed with asthma, some tests will be repeated on a scheduled basis to monitor treatments.

About asthma tests

Asthma tests are prescribed for individuals who are suspected of having asthma or to monitor the treatment of this condition. Asthma is an obstruction of the lower airway, caused by inflammation, mucus clogging and muscle spasms around the bronchial tubes.

Exposure to allergy triggers often produces symptoms such as chronic coughing, wheezing and breathing problems. In rare cases, a severe asthma attack can be fatal.

Tests used in the diagnosis and treatment of asthma fall into two categories:

  1. Assessing lung function
  2. Identifying allergens or other triggers that may lead to an asthma attack

Lung function tests

Assessing how well the lungs and respiratory system function is an important step in the diagnosis of asthma. The same tests may also be used to monitor the effectiveness of asthma treatments. Tests commonly used to assess lung function include:

  • Pulmonary function test. One of the most commonly used methods to measure an individual’s breathing efficiency. This five-phase test makes frequent use of a spirometer, which features a tube and a recording device designed to gauge the volume of air inhaled and exhaled by an individual, and calculates the length of time between each breath. These tests also measure:

    • Maximum volume ventilation (MVV). Measures the complete volume an individual exhales in a 15 second period. This number is multiplied by four to find the value for one minute.

    • Forced vital capacity (FVC). Measures the volume of air exhaled over a continuous period up to six seconds. This helps provide an indication of how much air the lungs can hold.

    • Forced expiratory capacity (FEV1). Measures the speed of air exhaled in one second.

      Some phases of a pulmonary function test can be done in the home, while other parts must take place at a medical facility using specialized equipment.

  • Gas diffusion test. A type of test that measures the amount of oxygen and other gases that cross the alveoli in one minute. This test may be performed if a physician suspects that another condition may also be present, such as chronic obstructive pulmonary disease. This type of test includes:

    • Arterial blood gas analysis (ABG). Used to assess lung efficiency by measuring the concentration of oxygen and carbon dioxide in the blood drawn from an artery (vessel that carries blood from the heart to the tissues). These are important measures, because they tell a physician how efficiently a patient is inhaling oxygen into the body, and exhaling carbon dioxide into the air. The body’s cells use oxygen to do their work, but in doing so they create carbon dioxide as a byproduct. Carbon dioxide is toxic at certain levels and must be expelled from the body. A poor ABG result might indicate an asthma diagnosis.

    • Carbon monoxide diffusing capacity. Measures how efficiently the lungs can transfer a small amount of carbon monoxide into the blood. A small amount of carbon monoxide is inhaled and tests evaluate how well the gas can move from the lungs into the blood.

  • Peak flow meters can be used by patients to check their own lung function from the comfort of their own home. This device measures the force of breath during inhalation and exhalation. By using a peak flow meter each day, patients can detect changes in their breathing capacity before the condition manifests itself in asthma symptoms. Peak flow meters can also help an individual determine the severity of an asthma attack once it has begun.
  • Body plethysmography. In this technique, a patient sits inside a clear, enclosed chamber and breathes on a mouthpiece. A computer measures how the chest wall alters the volume of gases inside the chamber as an individual inhales and exhales. This allows the computer to gauge the amount of gas left in the lungs at the end of a normal exhalation. Plethysmography often is used with a bronchoprovocation because it can detect very subtle changes in the airways.

  • Pulse oximetry test. Measures the amount of oxygen in the blood. A computer reads information transmitted by a probe attached to a patient’s ear or finger.  A pulse oximetry test is faster and easier to obtain than an arterial blood gas analysis, but not as accurate.

  • Bronchoscopy. A procedure that uses a bronchoscope to examine the airways leading to the lungs. A thin, lighted instrument is inserted through the nose and mouth and threaded to the airways. This test may be performed to rule out other conditions that may mimic the symptoms of asthma.

Most tests of the lungs present little or no risk to the individual being tested unless they have a serious heart or lung condition. Those who do should talk to their physician. Patients who have blood drawn during an arterial blood gas analysis may feel lightheaded, dizzy or nauseous and may have bruising around the puncture site. Continued bleeding can be a concern for those with bleeding disorders. Rarely, a needle can damage a nerve or artery, causing a blockage.

Since young patients often have difficulty following the instructions given during lung testing, children under the age of 5 cannot usually perform lung function tests. Instead, a physician will often base an asthma diagnosis on the patient’s clinical signs and symptoms, as well as the information collected from a medical history and physical examination. The physician may prescribe a bronchodilator for the child and confirm the diagnosis if the child’s signs and symptoms improve with its use.

Trigger identification tests

Once a person has been diagnosed with asthma, it is important to identify those factors that may trigger an asthma attack. Since people with asthma are more likely to also have one or more allergies, one or more allergy tests may be performed, including:

Allergy skin tests. A small amount of an allergen is introduced to the patient’s skin. If a rash develops, the patient is most likely allergic to that substance. Allergens may be introduced to the skin by prick, scratch, patch or injection to provoke a reaction. However, these tests are not 100 percent accurate and skin testing is not practical for those with certain skin conditions (e.g., eczema, psoriasis).

RAST (radioallergosorbent test). This type of blood test allows a laboratory to directly test a blood sample for antibodies that correspond to specific allergens. While less sensitive than a skin test, it can be used on individuals who have reactions too severe for a skin test.

Bronchoprovocation test. A test that involves inducing a mild asthma attack to diagnose asthma when symptoms are not present. Most bronchoprovocation tests are performed by inhaling histamine or methacholine to induce asthma symptoms. This test can be helpful in confirming a diagnosis. A bronchoprovocation test may also involve other specific agents, such as food additives or environmental allergens, or may involve exercise (exercise challenge test). Because of the potential risks of inducing an asthma attack, this test is always performed under close supervision by medical personnel.

Other related tests

A number of other tests may be performed when asthma is suspected, primarily to rule out other potential causes of breathing problems, such as chronic obstructive pulmonary disease (COPD), pneumonia, bronchitis, pulmonary embolism and heart failure. Tests may also be performed to screen for a condition that commonly occurs in conjunction with asthma, such as gastroesophageal reflux disease (GERD), allergic rhinitis (hay fever) or rhinosinusitis. These tests may include:

  • Chest x-ray. Uses low doses of radiation to produce an image of the chest.

  • Sinus x-ray. Uses low doses of radiation to produce an image of the sinuses.

  • Sputum examination. Uses a microscope to analyze a sample of sputum (phlegm coughed up from deep inside the lungs).

  • Echocardiogram. Uses sound waves to create a picture of the heart.

  • Electrocardiogram (EKG). Records the electrical activity of the heart.

  • Stress test. Takes EKG readings of the heart while a person exercises.

  • CAT scan of the chest. Creates a picture of the chest and upper abdomen.

  • CBC (complete blood count). Determines the counts of various types of blood cells.

  • Gastroesophageal reflux assessment. May include a number of diagnostic tests for GERD, including barium swallow (a test in which an x-ray is taken after liquid barium is ingested) and esophageal pH monitoring (involves passing a thin tube attached to a monitoring device through the nose and into the esophagus where it records the amount of stomach acid that reaches the esophagus).

Treatments that may follow asthma tests

If testing indicates a diagnosis of asthma, a physician is likely to classify the asthma into one of four categories, and to treat the condition accordingly. The four conditions of asthma are:

  • Mild intermittent. Symptoms appear up to two days a week and two nights a month.

  • Mild persistent. Symptoms appear more than two nights a month and more than twice a week, but not more than once in a single day.

  • Moderate persistent. Symptoms occur every day and more than one night a week.

  • Severe persistent. Symptoms occur continuously throughout the day and frequently at night.

Periodic testing following a diagnosis may be used to re-classify a patient whose asthma symptoms have worsened in frequency or intensity. This is important because the various medications and treatments for asthma are determined, in part, by the category of the patient’s asthma.

For instance, asthma medications fall into two categories:

  • Quick-relief medications. These are designed to instantly relieve the symptoms of an asthma attack. Patients with mild intermittent or mild persistent asthma may receive a quick-relief medication to aid them when their asthma flares up.

  • Long-term-control medications. These are designed to minimize inflammation and prevent asthma flare-ups before they occur. Those with moderate or severe asthma are more likely to need both quick-relief and long-term-control medications.

Management of asthma over time includes using medications properly, as well as reducing the risk of asthma attacks. This includes:

  • Reducing exposure to environmental triggers, such as pollens, molds, secondhand tobacco smoke and animal dander.

  • Encouraging a healthy lifestyle that includes proper rest, good nutrition and regular exercise.

  • Combating obesity. For reasons not fully understood, there appears to be a correlation between obesity and increased incidence of asthma.

Questions for your doctor about asthma tests

Preparing questions in advance can help patients to have more meaningful discussions with their physicians. Patients may wish to ask their doctors the following questions about asthma tests:

  1. What tests will you use to determine if I have asthma?
  2. What tests will you use to determine the factors that trigger my asthma?
  3. Will I require additional testing to monitor my asthma? If so, how often?
  4. Will I be required to test myself at home?
  5. How accurate are the asthma tests I will be undergoing?
  6. Are there any risks associated with the asthma tests I will be undergoing?
  7. Will I experience any pain while undergoing the test?
  8. Are there any special steps I should take to prepare for my asthma test?
  9. When will my tests results be available? Who will explain them to me?
  10. What do the results of my asthma testing indicate?
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