Methacholine Challenge Test?

Question

Has anyone ever had this test? My Dr. has scheduled this test for me this Friday. But I am already diagnosed with asthma and don't really understand the point of the test. I have bad allergies, which are the main cause of my asthma. I take Singulair once daily, which seems to help a lot. But I still have some impairment with my lungs. I am a little nervous about taking this test.

Thanks for your answers guys!

Answer 1

To answer your question simply, It could be that your doctor wants to see if the diagnosis is right. Or, insurance/medicare will pay for this test to be done several times. So it could be just another money maker for your doctor. You may want to ask him why. Good luck.

Answer 2

Methacholine Challenge Test Interpretation

Answer 3

Methacholine Challenge Interpretation

Answer 4

This Site Might Help You.

RE:
Methacholine Challenge Test?
Has anyone ever had this test? My Dr. has scheduled this test for me this Friday. But I am already diagnosed with asthma and don't really understand the point of the test. I have bad allergies, which are the main cause of my asthma. I take Singulair once daily, which seems to help a lot. But I...

Answer 5

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Answer 6

Methacoline test is not only for diagnosing asthma, it is also to determine your asthma severity.

Answer 7

Methacholine Challenge


What is methacholine challenge?
Methacholine challenge is a diagnostic test for asthma. It is one way of evaluating the reaction of the airway to potential triggers of asthma attack. Methacholine is a synthetic chemical related to the natural neurotransmitter acetylcholine. It induces constriction of the bronchial tubes leading to the lungs. The technique is based on the premise that asthmatics are more sensitive to the effects of the drug.

Additional uses of the test would be for assessment of:
The Effectiveness of Asthma Medications
A Person's Risk for Developing Asthma in the Future
Research shows that even though they do not yet have any symptoms of asthma, up to 45% of individuals who are markedly susceptible to methacholine will subsequently develop asthma (within two to three years time).

How is the test done?
Methacholine challenge assess response to progressively-stronger doses of methacholine, in the following manner:

The patient puts on a nose clip (worn to restrict air flow to the mouth).
Step 1: A baseline measurement is taken of the maximum forced expiratory volume (FEV) the patient is capable of blowing out after breathing in fully.
Step 2: The patient slowly inhales a deep breath of methacholine vapor from a nebulizer.
The patient holds his/her breath for five seconds to enable the methacholine to penetrate the lungs.
Steps 3-6: The patient takes four more full breaths of methacholine, holding them in each time.
Step 7: After a 30-second delay, the FEV is re-measured.
Step 8: After waiting about a minute longer, the FEV is again measured.
The technician moves on to the next-highest dose. Steps two through eight are repeated for each dose.
(A total of five different concentrations of methacholine are used, unless a positive response has already been seen at a lower dose.)
At the conclusion of the test, a bronchodilator is given.
(The bronchodilator counteracts the effects of the methacholine.)
Ten minutes later, FEV is measured one final time.
[Note: Protocols may vary slightly, including the specific concentrations of methacholine used and the exact number of breaths taken.]

Who needs a methacholine challenge?
Methacholine challenge testing is appropriate for someone who:

Has had a negative result for asthma screening
[as evaluated by change in forced expiratory volume in response to administration of a bronchodilator, typically albuterol (i.e. the patient exhibited little or no improvement in lung capacity after the asthma medication was given)],
even though the person experiences characteristic symptoms of asthma (e.g. cough, wheezing, or tightness in the chest).
[Alert: Certain patients should not undergo methacholine challenge.]

Who shouldn't have methacholine challenge done on them?
Those for whom methacholine challenge would be risky are patients:

With an Aneurysm
Who Have Had a Heart Attack or Stroke within the last three months
With Chronic Hypertension (uncontrolled)
Who Are Using a Cholinesterase Inhibitor (a medication for myasthenia gravis)
Possibly for Pregnant or Nursing Women

Why-- is methacholine challenge dangerous?
For most patients, any risk of methacholine challenge is minimal.

Mild asthma symptoms may be experienced (side effects are primarily cough, chest tightness, and wheezing)
However, in the case of severely restricted lung capacity, the test is not recommended.

What is a good score for the test?
Exposure of the lungs to methacholine constricts the lungs, thereby the higher the dose of methacholine, the lower the FEV will be. The data is plotted on a graph. By connecting the data points, FEV can be estimated for any concentration of methacholine that falls in between the specific doses given. In reviewing the results, the doctor looks for the concentration of methacholine that lead to a drop in the FEV of at least twenty percent below its usual ("baseline") amount.

If it took greater than 16 mg/ml of methacholine in order to induce a 20% drop in the FEV, that would be interpreted as proof that the individual does not have asthma.
On the other hand, demonstrating a 20% decrease in FEV for any concentration of methacholine below 1 mg/ml is regarded as being a positive test for asthma.
Results that fall between 1 mg/ml and 16 mg/ml are considered to be less conclusive.
(Some doctors consider 8 mg/ml to be the cut-off that divides people who have asthma from those who do not.)
Factors that the doctor takes into account when interpreting the test results are:
Asthma symptoms experienced by the patient during the test, as well as beforehand
Extent to which the bronchodilator taken after the test alleviates the patient's symptoms
The amount of baseline airway obstruction (whether the patient had a low initial FEV)
Reproducibility of the test (the ability to repeat the procedure at a different time with similar results)

How accurate is methacholine challenge?
If asthma is present, the test will almost always reveal excessive bronchoconstriction; that is, non-response to methacholine would be an almost sure sign that the patient does not have asthma, regardless of any asthma-like symptoms that s/he may be experiencing. Thus, methacholine challenge is quite useful for ruling out asthma.

On the other hand, the test is less reliable for confirming a diagnosis of asthma.
Another limitation of the test is that it is difficult to interpret with certainty when the patient had a low FEV to begin with (since in order to note response, the FEV must drop substantially)
[Note: The nebulizer equipment must be properly calibrated and maintained, in order to ensure that the dose it dispenses is accurate.]

Why wouldn't the doctor definitely be able to tell from the test if I have asthma?
The main reason is that conditions other than asthma can also cause hyper-responsiveness to methacholine.

In other words, the drop in FEV can be significant when in fact the patient does not actually have asthma. Therefore, despite the positive test result, whether or not the patient has asthma remains questionable.
(Unless just a small amount of methacholine produced pronounced bronchoconstriction, in which case the probability of asthma is high).

Which other diseases would make the result come out positive?
Accuracy of the test presumes that the patient is not on any medications that would mask the response, namely asthma medications or other potent anti-inflammatories. Disorders other than asthma that can produce a positive outcome for methacholine challenge are:

Chronic Obstructive Pulmonary Disease
Congestive Heart Failure
Cystic Fibrosis
Bronchitis
Allergic Rhinitis
Additional conditions would be:

Exposure to Other Sensitizers, such as
Pollutants
Work-Related Chemicals

And, to a lesser extent:
Recent Colds (up to six weeks prior)
Smoking (influences outcome to an uncertain extent)
Consumption of Caffeine (only on the day of the test)

What is the other kind of test that can be used instead?
The other airway response test in widespread use is exercise challenge.

(Some individuals have exercise-induced asthma, yet do not respond to methacholine challenge.)


Sources: American Academy of Asthma, Allergy,
and Immunology
American Journal of Respiratory and
Critical Care Medicine