A Methacholine is ordered to find out if your breathing problem is from asthma. Or, to see if your asthma is under control.
What to Expect
- A baseline spirometry test will be performed. If your lung function is not too low, you will move to the next step.
- You will be asked to breathe in a very low dose of methacholine.
- You will repeat the spirometry test immediately after inhaling the methacholine and again a few minutes later.
- If your lung function does not change after the lowest used dose of methacholine, you will inhale the next higher dose of methacholine that is a little stronger than the first does. You will then do spirometry again.
- As long as you do not react to the methacholine, you will continue the test, inhaling stronger doses of the chemical (usually 5-10 doses total) followed by spirometry testing.
- As soon as your lungs show a significant worsening in lung function, with a drop in forced expiratory volume at 1 second (FEV1) of 20% or more, the test is considered complete. You will be given an inhaled bronchodilator treatment (usually albuterol or levalbuterol) to help re-open your airways. You will then repeat the spirometry test to make sure your lungs have returned to normal. The concentration of the methacholine given at this point will be your test result. If you do not have a drop in function or symptoms, the last dose given is the result.
- You will not leave the test area until your breathing has returned to normal. You may therefore be asked to wait for an hour or more, before being allowed to go home.
How to Expect to Feel:
The Methacholine challenge test is designed to see if your airways tighten, so if your airways do not tighten, you may have no symptoms at all. If your airways do tighten during the test, you may have symptoms of an asthma worsening. You may cough, wheeze, feel chest tightness or be short of breath. If the test results show that your airways are tightening, you will be given a bronchodilator that will relieve the symptoms. The test is done in a testing center with trained staff and a physician is available during the study.