A bronchoprovocation test is an attempt to provoke mild bronchospasm (narrowing of the airways caused by muscle contraction) in patients in a controlled setting. In most tests, substances such as histamine and methacholine are introduced to see if the patient’s airways constrict. The test is used to help diagnose or rule out asthma as the cause of respiratory problems.

The exercise challenge test is another common bronchoprovocation test. This is used to diagnose asthma in individuals who experience symptoms that appear to be triggered by exercise.

Bronchoprovocation tests can confirm (or rule out) the presence of airway hyperresponsiveness (easily irritated breathing passages), as well as determine the severity of the disorder. Test results can also provide a foundation for an effective treatment plan. However, these tests present very slight but potentially serious health risks and should only be performed by trained healthcare professionals in a medical facility.

Asthma is not the only disorder that causes bronchial hyperresponsiveness. Chronic obstructive pulmonary disease (COPD), heart failure, cystic fibrosis and bronchitis also cause this condition. For this reason, bronchoprovocation testing is a more effective tool for ruling out an asthma diagnosis than for specifically identifying asthma as the cause of breathing problems (e.g., coughing, shortness of breath). 

A bronchoprovocation test induces airway symptoms in a patient for the purpose of identifying or ruling out asthma as the cause of respiratory problems. These tests are used when asthma is considered likely, but the diagnosis has not been confirmed by traditional pulmonary (lung) function testing.

During a bronchoprovocation test, the patient will be exposed to a substance – histamine or methacholine – to determine if it causes the airways to narrow and spasm. If the substance triggers bronchospasm (narrowing of the airways caused by muscle contraction), then a diagnosis of asthma is probable. However, a physician will perform other tests to confirm the diagnosis. Because methacholine is so widely preferred in bronchoprovocation testing, the procedure often is referred to as a methacholine challenge test. Histamine is used less often because it often triggers headaches and flushing.

During the test the patient inhales a steadily increasing amount of methacholine in aerosol-mist form both before and after testing with a spirometer (a device which records the patient’s breathing capabilities). If lung function drops by 20 percent, asthma is considered likely.

The exercise challenge test is another bronchoprovocation test. It is used to diagnose asthma in individuals whose symptoms appear to be triggered by exercise.

Bronchoprovocation testing is highly sensitive and is an excellent device for detecting bronchial hyperresponsiveness, or easily irritated airways. It can also be used to determine the severity of the disorder. However, the test is not as effective at identifying the specific source of airway constriction. Asthma is not the only disorder that causes bronchial hyperresponsiveness. For this reason, bronchoprovocation testing is a more effective tool for ruling out an asthma diagnosis (if a patient’s breathing capacity does not diminish by more than 20 percent) than for specifically identifying asthma as the cause of breathing problems. Other asthma tests will be performed to confirm a diagnosis of asthma.

Other causes for bronchial hyperresponsiveness include:

• Chronic obstructive pulmonary disease (COPD). A chronic, progressive disease of the lungs that reduces airflow over time. Symptoms include coughing, wheezing and shortness of breath.
  
  
• Bronchitis. An inflammation in the lower airway of the respiratory system. Symptoms include a cough that produces mucus, shortness of breath and wheezing.
  
  
• Cystic fibrosis. A disease that causes the body to produce thick, sticky mucus that builds up in the lungs. Symptoms include chronic coughing, regular episodes of bronchitis and pneumonia and persistent wheezing.
  
  
• Heart failure. A chronic condition in which the heart is not pumping efficiently. Symptoms include shortness of breath, swelling of the feet or legs and swollen neck veins.

Although bronchoprovocation tests can be used to assess airway responsiveness in children, the test is most often used in adults. Bronchoprovocation tests may also be used to evaluate occupational asthma (asthma triggered by exposure to dust, vapors, gases, fumes or other irritants at a patient’s workplace), determine a patient’s risk of developing asthma or assess a patient’s response to treatment.

Patients scheduled to undergo bronchoprovocation testing should clear their bodies of all asthma and other pulmonary (lung) medications. For example, a patient who has a 4 p.m. test should not take a short-acting bronchodilator (which lasts four to eight hours) any later than 8 a.m. that morning. This rule should also be applied to all other similar medications. However, patients should consult with a physician before modifying medication intake.

Patients should also avoid the following on the day of the test:

• Chocolate
• Coffee, tea, cola drinks or other caffeinated beverages
• Smoking (for at least six hours prior to testing)
• Environments that are extremely cold or extremely hot
• Exercise

Patients need to be free from respiratory infections for six weeks prior to their testing date. Patients who have viral infections should not participate in bronchoprovocation testing until they are well and their lung capacity returns to normal.

Patients who have recently suffered a heart attack or stroke and those with aneurysms (a bulging out of part of the wall of a blood vessel) or uncontrolled hypertension (high blood pressure) are also considered poor candidates for bronchoprovocation testing. In addition, pregnant women may be advised to postpone testing, as the effects of methacholine on the fetus are unknown.

The bronchoprovocation test is usually administered either at a physician’s office or clinic on an outpatient basis.

Just prior to the test, patients undergo pulmonary (lung) function testing with a spirometer (a device which records the patient’s breathing capabilities). This establishes a patient’s fitness for the bronchoprovocation test, and provides a baseline measure to which test results will be compared.

The key measure of bronchoprovocation testing is force expiratory volume (FEV). FEV is the amount of air exhaled forcefully in a sustained breath over a given period of time. Fitness for bronchoprovocation testing depends on the patient’s force expiratory volume at 1 second (FEV1). Patients who fail to meet threshold standards for good respiratory health are unlikely to be allowed to participate in the bronchoprovocation test. Some factors that may exclude a person from taking the test include:

• Decreased ventilatory function as a result of withholding medication
  
  
• Adults with FEV1 readings of less than 1.5 liters and children with FEV1 readings of less than 1 liter
  
  
• A response of 10 percent or more to the substance used to dilute the reactive substance

If a patient can take the test, the main form of testing is through exposure to histamine or methacholine (methacholine challenge test). A nebulizer (a device that breaks down liquid medicine into an aerosol mist) is used to deliver the “challenge” substance to the patient at intervals based on one of two methods:

• Two-Minute Tidal Breathing Method
  
  
  • The patient first will be exposed to a substance (usually saline) used to dilute the reactive substance. Two minutes later, another pulmonary test will be performed. No effect on the patient’s breathing capacity should be detected. In this way, the saline acts as a placebo, ensuring that emotional or psychological factors are not playing a role in any reaction that might take place to the “challenge” substance.
    
    
  • Next, the lowest dose of the testing substance – either histamine or methacholine – is introduced. After two minutes, another pulmonary function test is performed. If the patient’s FEV1 has not fallen by at least 20 percent, a higher dose of methacholine is introduced (up to a maximum dose of 16 milligrams per milliliter [mg/mL]).
    
    
  • If the test does not provoke a 20 percent decrease in FEV1, the patient is not likely to have asthma.
    
    
• Five-Breath Method
  
  
  • The patient is exposed to the testing substance and uses five deep breaths to inhale it.
    
    
  • A pulmonary function test is performed and the patient’s FEV1 is checked to see if it has fallen by at least 20 percent. If it has not, the test may be repeated with higher doses of the “challenge” substance (up to a maximum dose of 16 mg/mL).
    
    
  • If the test does not provoke a 20 percent decrease in FEV1, the patient is not likely to have asthma.
    
  
  

Individuals may experience a variety of complications during the test, including severe coughing, dizziness, light-headedness and chest pain. Patients experiencing discomfort or breathing difficulties at any point during testing should alert the technician who is administering the test. 

At the end of testing, a bronchodilator (a medication that expands the airways and improves breathing) will be given to the patient to reverse any constriction of the airways that has taken place. The patient will undergo one last round of pulmonary function testing to ensure that lung capacity has returned to normal. The entire testing process takes about 90 minutes.

Exercise challenge tests are similar to the basic bronchoprovocation test but add a component of exercise. The patient undergoes baseline pulmonary function testing before exercising on a treadmill or exercise cycle for about 10 minutes. The exercise should closely resemble the form of activity that most often triggers the patient’s symptoms. Once exercise concludes, pulmonary function testing is again performed. The process is repeated until either the FEV1 level drops by more than 20 percent, or 30 minutes elapse.

Bronchoprovocation testing is usually very safe when performed by trained healthcare professionals in a medical facility. However, since these tests are designed to provoke an allergic reaction, there are some risks.

By their very nature, bronchoprovocation tests induce mild bronchospasm (narrowing of the airways caused by muscle contraction), which can be more severe in some patients. However, medications that open the airways will be administered after testing to ensure that the patient’s breathing returns to normal and remains that way.

The biggest risk with bronchoprovocation tests is the possibility of anaphylactic shock, a potentially life-threatening allergic reaction to a substance. This is very rare, but it has occurred, and it requires an immediate dose of epinephrine (adrenaline) to reverse symptoms. Because of the slight but very real danger of anaphylactic shock, no patient should undergo bronchoprovocation testing unless under the supervision of a healthcare professional with immediate access to epinephrine. The testing staff should also have access to oxygen, and should be trained in CPR (cardio pulmonary resuscitation).

If bronchoprovocation tests indicate an asthma diagnosis, a physician may recommend several steps to treat symptoms of the disorder.

Once an individual has been diagnosed with asthma, a physician will develop an asthma action plan to help the patient monitor the condition. A typical plan will contain the following elements:

• A list of specific symptoms that often precede an individual’s asthma attacks
  
  
• Steps to take during an attack
  
  
• How to recognize a serious attack, and what to do about it
  
  
• How to recognize an emergency
  
  
• Changes in environment and behavior that can reduce the chances of an asthma flare-up

Current asthma treatment focuses primarily on preventing or reducing the inflammation process, and relaxing the smooth muscle that tightens during bronchospasm (narrowing of the airways caused by muscle contraction). Patients with mild intermittent or mild persistent asthma may receive a quick-relief medication to aid them when their asthma flares-up. Those with moderate or severe asthma are more likely to need both quick-relief and long-term-control medications.

There is no cure for asthma. However, there are several things that people can do to reduce the symptoms of asthma that make breathing difficult, including:

• Reducing exposure to environmental triggers, such as pollens, molds, secondhand tobacco smoke and animal dander.
  
  
• Leading a healthy lifestyle that includes proper rest, good nutrition and regular exercise.
  
  
• Taking all asthma medications as directed.
  
  
• Combating obesity. For reasons not fully understood, there appears to be a correlation between obesity and increased incidence of asthma. Obese individuals who lose weight often shed symptoms of asthma as well.

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 bronchoprovocation tests:

1. Why are you recommending that I undergo a bronchoprovocation test?
   
   
2. Can you explain the test to me in detail?
   
   
3. Are there special steps I should take on the day of the test?
   
   
4. How long will the bronchoprovocation test take? Where will I have to go for the test?
   
   
5. Will I need someone to accompany me to the test, or to drive me home after the test?
   
   
6. Will I be able to resume my normal activities after testing?
   
   
7. What risks do I face by undergoing this test?
   
   
8. What will happen if I have a reaction during the test?
   
   
9. When will I receive the results of my bronchoprovocation test? Who will explain them to me?
   
   
10. How accurate is this test? Can I trust the results?
    
    
11. What will be the next step if my results indicate asthma?