Q&A About the Methacholine Challenge

Here's part of a comment I got asking about the methacholine challenge.

"I too fall into the peak flow readings of way above average. So, because of this and even when feeling bad I still managed 110% of predicted on PFTs, and a methacholine challenge test that was originally read as "yes, you do have asthma" (that's what that pulmo told me), then 3-4 weeks later he changed his mind and said it was not indicative of asthma.

Add to all that, my current pulmo (who's actually not bad) keeps telling me that he doesn't think it's asthma, but keeps putting the diagnosis every visit as "asthma". I had to push for trying symbicort, which we discovered really helps me, and for trying singulair again...

Ok, for one more question.... about the methacholine challenge.... could you expand on that?"

So here goes, the methacholine challenge... It is not my area of expertise, I barely paid any attention to it until the asshole allergist tried to kill me with it.

I tried not to write a book, but you know what? There's a lot to this stuff. Hopefully I made it an entertaining read.

The Basics of the Methacholine Challenge

The test itself is relatively simple, if a bit of a workout. There's a lot of heavy breathing.

There are nose clips involved too which are not so fun, or at least I don't like them. You breathe in and out of a tube with varying levels of super human effort at the direction of a respiratory therapist who doses you with an odorless tasteless irritant until your lungs react.

Feeling a little light headed is common.

Asthma can be triggered too. I had a big spasm of something in my lungs during my supposedly negative methacholine challenge.

Aside from the tube, some places actually have a 'gas chamber' you sit in and they gas you and see how your airways respond. I had the chamber the first time around.

After the test, you either get a rescue inhaler to take or a nebulizer treatment to reverse the effects of the challenge. You should be fine to go back to normal activities, but, in my experience, the asthma exacerbation can persist a bit past the test.

A Positive Methacholine Challenge Means Nothing

A positive methacholine challenge is indicative of asthma, although doctors are cautioned to not jump to any conclusions since, apparently, it still could not be asthma. Here's what they are looking for in terms of asthma:

"A positive test is defined as a decrease from the baseline forced expiratory volume in the first second (FEV₁) or of the postdiluent FEV₁ value of 20%, or of a decrease in specific conductance of 35-45% from the baseline or post-diluent value." (Source: AARC Clinical Practice Guideline)

FEV1 is kind of like a peak flow measurement. So just like your peak flow/lung capacity drops when you are sick, the FEV1 will do the same when they dose you with enough irritant.

So when you see your doc after a methacholine challenge the question you ask is, "How much did my FEV1 drop?" AND then you get a copy of the test and immediately tattoo the damn thing to your chest so it's the first thing they see in the ER.

When a doctor says the methacholine is positive, but then also says you don't have asthma,well they are mentally challenged. Why? Because, with few exceptions, other causes for a positive challenge are nowhere near serious enough to result in ER visits and the misery of asthma. Here's a list of what other conditions may result in a positive meth challenge:

-COPD (which is like asthma's hot twin sister)
-Chronic cough
-Allergic Rhinitis
-Smoking
-Active respiratory infection
-Congestive heart failure

These issues, in my limited experience, have alternate diagnostic methods and a unique progression that is different from asthma. They would not look like asthma for very long before other symptoms or complications appeared.

I am actually kind of underwhelmed about the coughing and smoking. I mean, really? Are you people serious? You can be a smoker and have asthma. You can have a cough as the primary asthma symptom. I don't know, this is just weird.

As for COPD, it is treated with many of the same meds as asthma anyway. The issue becomes more about refining the diagnosis and picking the right therapy than denying care. At least that's my uneducated take on it.

I could pick and pick and pick at this list and why it should not seriously complicate an asthma diagnosis, but it would take too long. Just let me reiterate that I am underwhelmed with medical science here.

The differential diagnosis list for asthma is a bit more impressive by comparison. That is a scarier list with things like pulmonary embolism on it that you definitely want ruled out. The asshole allergist pulled a few items off this list, that were life threatening, and told me that could be my problem. Then she sent me on my merry way with no follow up care which was unethical and negligent.

That was the point I started documenting the asshole allergist's crazy and told my husband who to sue if I up and died.

Negative Methacholine Challenge & False Negatives

Now, a negative methacholine challenge means you will never ever have asthma. Ever. Plus, you are a big fat fatty faker hypochondriac. Except when you're not and when you do have asthma.

The test is not perfect, despite what doctors may think. False negatives do happen. Some people's airways are just funky, but good luck getting any doctor to agree on that point.

The methacholine challenge can also be f*cked with. In my experience, the results can be affected by poor pre-testing instructions regarding when to discontinue medication.

Inhaled steroids can stay in the system for a while. In fact science isn't sure exactly how long they persist after you stop taking them. If you aren't off steroids long enough (inhaled or oral), the methacholine challenge will be a bust. Long acting bronchodialators require abstention for up to 48 hours or they can affect the test. Medications like Singulair should be discontinued 24 hours before the test. Other medications have a different abstention schedule which you can view in the AARC Clinical Practice Guideline linked above.

The National Jewish Center for Immunology and Respiratory Diseases (the experts in asthma) makes the same recommendations.

Other individual doctors have different approaches. I've seen some that say to stop inhaled steroids for just 12 hours prior to the test, but they are not large, cutting edge research institutions and I would end up arguing with them if I was their patient. They would not like me and I would blog mean things about them.

What happened with my last methacholine challenge was the asshole allergist did not properly instruct me on when to discontinue my medications. I only missed one dose and was without medication for only about 9 hours in total. That's like sleeping in on a weekend. It's zero risk.

Today, I bet the test would be positive anyway because my airways are so reactive now, since March. However, back then? I was stone cold controlled. There was no way, no how that missing one dose of my meds would've done anything, not when my control was so good.

I was also taking a pretty good dose of inhaled steroid, 1000 mcg a day and it is well established that regular use of inhaled steroids decreases airway sensitivity. Which can muck up a test that relies on airway sensitivity.

When I raised holy hell with the HMO and pointed out the AARC guidelines, they admitted the protocol was not good and offered to do another test with another doctor. I ignored them because, as I've mentioned before, I was so disgusted I refused to have anything further to do with them.

If I had it to do over again, I would've made sure I was nice and sick when I showed up for the test. Stopped my meds a week earlier, that kind of thing. Just so there would be no doubt. Although it's a risk to take when you are the primary care giver of a small child and need to be healthy.

When I had the test years and years ago, I wasn't on any medications like Advair or Singulair yet so it was not a big deal. If memory serves, my FEV1 was kind of borderline at 17%, but I somehow had a decent doctor who decided I had asthma anyway (thank goodness). Probably because she could hear me wheeze and creak without a stethoscope.

By the time your lungs creak like a haunted house, doctors are a bit more on board with asthma.

The only problem is getting sick enough for them to Get A Clue. Also, remember the diagnosis is non-transferable and they can change their mind at any time. Which sucks. It happened to me and it can happen to you.

I have no idea how patients can protect themselves other than to keep looking for a doctor, get copies of medical records and to scream and yell, hop up and down until doctors realize it's more dangerous for them to deny treatment than to continue it. Also, hoard your medication, that saved my sorry ass when I was battling the asshole allergist.

Anyway for more information, this article goes into how the challenge is used to rule out asthma and why the test is not considered diagnostic. I could spend hours picking it apart, but I won't. Suffice it to say I have a really hard time believing congestive heart failure is such an elusive diagnosis that it would cause patients to be parked on asthma for years and years.

The kicker about this article is that 'asthmatics' don't seem to get a positive result almost half the time. The assumption is then made that the patients must have something else, not that maybe the test is not really effective. False negatives are mentioned, but not elaborated on, which is unfortunate. This author, in my opinion, has a bias that would hurt patients like me.

However, here's a great quote on false negatives with the methacholine challenge from the American Thoracic Society. It's in medicalese, so you need to look at it funny to properly read it.

"Three factors should be considered before accepting a negative test as ruling out asthma: (1) airway responsiveness may have been suppressed if the patient was taking intensive antiinflammatory medications prior to the MCT. This issue may not be relevant if the patient has current symptoms; (2) in patients without current symptoms, the season for aeroallergen exposure may have passed (173, 174); and (3) a small fraction of workers with occupational asthma due to a single antigen or chemical sensitizer may respond only when challenged with the specific agent."

The Mayo Clinic Internal Medicine review on asthma and the methacholine challenge is also a pretty good read. Oh hey, look, this book is used to study for the boards, it says the test gives pretty high weight to pulmonary medicine meaning doctors really do study this stuff (unlike the poor, neglected adrenal glands).

Huh.

Except I notice the review does not explain how to properly prepare a patient for a methacholine challenge nor talk about false negatives nor how patient history still matters. I would assume, however, that this was covered by HMO policy staff and at some point during the asshole allergist's training. Or maybe that's just expecting too much.