What is the methacholine test?

The methacholine test is a test done for the purpose of diagnosing or ruling out asthma. Keep reading and know what the process is like and what should be taken into account before doing it.

Last update: October 29, 2021

The methacholine test is also known by other names, such as bronchoprovocation test or nonspecific bronchial provocation. It is done with methacholine or Provocholine ®, which is the brand of the product.

This exam is applied for the purpose of determining bronchial hyperresponsiveness. Consequently, diagnose asthma. During it, an amount of the referred medicine is inhaled, which causes a narrowing of the respiratory tract.

To perform the methacholine test certain previous precautions must be taken. For example, stop taking some medications or inhalers and avoid caffeine and cigarettes. Also, it should not be done during pregnancy.

What is the methacholine test and what is it for?

Bronchial hyperresponsiveness is a process that occurs when there is abnormal sensitization of the respiratory tract. This is due to an obstruction in the air flow, when the person is subjected to certain stimuli, such as pollen, dust, cigarette smoke.

During hyperreactivity, there is an exaggerated response of the bronchial mucosa that results in bronchospasm. This situation usually occurs in people with various respiratory conditions, such as asthma, bronchiolitis, even allergies and colds.

Now, in the methacholine test, this drug is used to induce hyperreactivity and thus observe how the lungs work. Methacholine chloride is a non-selective synthetic cholinergic agonist. Said compound activates muscarinic-type acetylcholine receptors, acting as a bronchoconstrictor. In particular, when inhaled, methacholine narrows the airways.



How is the methacholine test performed?

The process of performing the methacholine test takes about 90 minutes. It is divided into three phases or moments. The following describes each of them.

Moment 1

The test begins with a basal respiration assessment, also known as spirometry. This will help to know how the lungs are working in relation to variables such as the maximum expiratory volume in the first second, how fast is the breathing, how much air is inhaled and exhaled.

Spirometry is done at the beginning to determine the basal state of the lungs.

Moment 2

Using a nebulizer, inhaled methacholine is administered. This progressively increases until 4 doses are completed.

Before and after each one, spirometry is done again to measure the narrowing of the airways. Respiratory flow may stay the same, worsen, or improve.

Moment 3

When the maximum dose of methacholine predicted in the test is reached or if lung function decreases by 20%Based on the initial measurement, the test ends. Once finished, and if necessary, a bronchodilator (salbutamol) is administered.



How are the results interpreted?

During the test, various health professionals, familiar with the methacholine test or trained in it, may participate or be present. But it is the pulmonologist who is in charge of the assessment and interpretation of the results, as well as the preparation of the corresponding report.

In this order of ideas, the test can have two possible results. It is considered positive if methacholine causes lung function to decrease by 20% or more. Therefore, the person may have asthma.

Otherwise, if lung function is maintained or its decline does not reach such levels, the result is considered negative. Therefore, this disease can be ruled out.

Preparation for the methacholine test

Before performing the methacholine test, the person must provide various information to the professional or the medical team in charge of the test, in order to establish the measures to be followed.

This information has to do with any of the following factors:

  • Have ever had asthma symptoms.
  • Having suffered from a respiratory infection in recent weeks.
  • Being pregnant or nursing.
  • Having been immunized with a vaccine in the near future.
  • If you have any heart disease.
  • Allergic diseases, including various types of chronic urticaria.
  • Consumption of any medication for the respiratory tract.
  • If the person is a smoker or uses inhalers.

Discontinuation of medications and treatments

In case of taking drugs, some treatment may need to be stopped temporarily before doing the methacholine test, especially if the drugs in question have to do with the respiratory tract.

It is a good idea to discuss this with your doctor to find out which medications and for how long they should be stopped. Some only require a day or two of suspension and others a longer time.

It is emphasized that this should not be done on your own initiative, but under the guidance of the health professional. In addition, a doctor should be called if any reaction is observed after discontinuation.

The day of the test

Certain restrictions are imposed on the day on which the methacholine test is due. Among them, the most relevant are the following:

  • Stop using any type of inhaler for the treatment of asthma.
  • Avoid caffeinated drinks at least 6 hours before.
  • Do not smoke for at least 24 hours before the test.
  • Suspend bronchodilators between 12 and 18 hours beforehand.
  • It is recommended to only eat a light meal at least 2 hours before.
  • Do not exercise.

After the test

After the methacholine test, the person can resume their medications and return to their diet and regular activities. No recovery is required. Unless the doctor indicates otherwise.

Discontinuation of asthma inhalers should be done to properly assess the effect of methacholine.

Contraindications

The test should not be performed under certain conditions. In this sense, the methacholine test is contraindicated in some cases:

  • Pregnancy and breastfeeding.
  • Aortic or cerebral aneurysm.
  • Blood pressure problems.
  • Heart attack or stroke in recent months.

Some considerations when taking the test

The methacholine test it is minimally invasive and does not generate discomfort or side effects. However, some situations must be taken into account to prevent discomfort.

First of all, you have to remember that the test takes 90 minutes. Therefore, the person must be patient.

On the other hand, some efforts must be made. For someone who is not in good physical condition or who suffers from a respiratory disorder, the fact of inspiring and exhaling forcefully and quickly several times could cause dizziness, coughing, wheezing, pain in the rib cage, shortness of breath.

About, the person should inform the doctor if they notice any discomfort, if you feel unwell, if you need more time before spirometry, or if you think you need to stop the test. In the same way, if a situation arises days before that is thought to affect the result, it is advisable to contact the doctor.

It might interest you …