The Methacholine/HistamineChallenge
Enjoying yet another stay in the lovely hotel NHS and going a little stir crazy! One thing I notice a lot of people asking about in online support groups is what happens during a methacholine or histamine challenge test. I had one of these last summer and they sound very unpleasant so today I thought I'd write about my experience in the hope that it helps to put some worried minds at rest!
What is the test?
The methacholine and histamine tests are known as bronchial challenge tests. They're designed to irritate your airways and induce bronchoconstriction (which sounds awful!) which can then be measured.
They're often used to try and confirm or rule out a diagnosis of asthma in people where it isn't so certain - for example if you have normal spirometry but still have asthma symptoms.
Its carried out in hospital as an outpatient.
These tests are known as "direct" challenge tests as they directly irritate the airway. There are some other tests known as "indirect" challenge tests as they are designed to provoke bronchoconstriction by a different pathway.
What happens in the test?
First you'll do some baseline spirometry to see where you're at before the start of the test and then normally inhale a "control" substance (such as normal saline) through a nebuliser.
After this you will be asked to inhale differing concentrations of an irritant which is designed to inflame the airways and induce some bronchospasm. After this you do repeat spirometry to see how it has affected it.
The end point is either a reduction in spirometry by a certain amount (normally 20%) or running out of test concentrations. The results are then sent off for interpretion. Afterwards you're then given some salbutamol, either through a space or by a nebuliser until your spirometry is back to baseline.
What was my test like?
I was referred for mine because my airways were notoriously hyper-responsive and they wanted to see exactly how twitchy they were. I was also pretty worried about it despite not really being an anxious person as it sounds pretty horrendous and I couldn't really find any experiences of others online.
I had to stop my medications beforehand (make sure to check this with your department or online! As they can often forget to tell you what to stop which then affects the results), which given I have allergic asthma and it was peak pollen season was quite uncomfortable!
When I got there the person doing the test (a respiratory physiologist) took me through, asked me a bit about my asthma and explained the test to me in more detail. When I mentioned twitchy airways they said that they would make sure to start the test at a lower concentration than normal - so if you're worried because of this make sure to mention it as they'll take things like this into account.
We did my baseline spirometry and then I had some nebulised saline as a control test - this actually reduced my spirometry slightly so confirmed that we definitely needed to start low and slow on the methacholine!!
Then we started on the methacholine. I had this through a nebuliser and then had to do spirometry immediately after and then another couple of times after a few minutes. They also made a note of any symptoms they noticed in me (like coughing, of which there was lots!) and asked me about any subjective symptoms (like chest tightness).
Its a good thing we started low because I actually had a nearly 30% drop in my spirometry on the third concentration they tested - which was still lower than the standard starting dose would have been!
While it wasn't pleasant they were really lovely about it and I felt very calm and safe throughout the test. Its important to be aware that as soon as you hit that threshold the test stops and they give you salbutamol to reverse it. Once I'd had salbutamol my spirometry was quite a bit better than my baseline too - showing that I'd been struggling a bit before the test anyway!
Once they'd made sure everything was back to normal and I was ok I was sent off on my way. I didn't feel any residual symptoms, I was just tired out from doing a lot of spirometry! So I'd advise planning a quiet day afterwards!
Needless to say my test was pretty positive and although it was uncomfortable I'm really glad I got it done as it really helped to understand my asthma a bit more and made them take me a bit more seriously when I came in unwell.
I hope this has helped explain what happens to people and I'm happy to answer any questions people might have.
Here are a couple of links for some more info on the test:
What is the test?
The methacholine and histamine tests are known as bronchial challenge tests. They're designed to irritate your airways and induce bronchoconstriction (which sounds awful!) which can then be measured.
They're often used to try and confirm or rule out a diagnosis of asthma in people where it isn't so certain - for example if you have normal spirometry but still have asthma symptoms.
Its carried out in hospital as an outpatient.
These tests are known as "direct" challenge tests as they directly irritate the airway. There are some other tests known as "indirect" challenge tests as they are designed to provoke bronchoconstriction by a different pathway.
What happens in the test?
First you'll do some baseline spirometry to see where you're at before the start of the test and then normally inhale a "control" substance (such as normal saline) through a nebuliser.
After this you will be asked to inhale differing concentrations of an irritant which is designed to inflame the airways and induce some bronchospasm. After this you do repeat spirometry to see how it has affected it.
The end point is either a reduction in spirometry by a certain amount (normally 20%) or running out of test concentrations. The results are then sent off for interpretion. Afterwards you're then given some salbutamol, either through a space or by a nebuliser until your spirometry is back to baseline.
What was my test like?
I was referred for mine because my airways were notoriously hyper-responsive and they wanted to see exactly how twitchy they were. I was also pretty worried about it despite not really being an anxious person as it sounds pretty horrendous and I couldn't really find any experiences of others online.
I had to stop my medications beforehand (make sure to check this with your department or online! As they can often forget to tell you what to stop which then affects the results), which given I have allergic asthma and it was peak pollen season was quite uncomfortable!
When I got there the person doing the test (a respiratory physiologist) took me through, asked me a bit about my asthma and explained the test to me in more detail. When I mentioned twitchy airways they said that they would make sure to start the test at a lower concentration than normal - so if you're worried because of this make sure to mention it as they'll take things like this into account.
We did my baseline spirometry and then I had some nebulised saline as a control test - this actually reduced my spirometry slightly so confirmed that we definitely needed to start low and slow on the methacholine!!
Then we started on the methacholine. I had this through a nebuliser and then had to do spirometry immediately after and then another couple of times after a few minutes. They also made a note of any symptoms they noticed in me (like coughing, of which there was lots!) and asked me about any subjective symptoms (like chest tightness).
Its a good thing we started low because I actually had a nearly 30% drop in my spirometry on the third concentration they tested - which was still lower than the standard starting dose would have been!
While it wasn't pleasant they were really lovely about it and I felt very calm and safe throughout the test. Its important to be aware that as soon as you hit that threshold the test stops and they give you salbutamol to reverse it. Once I'd had salbutamol my spirometry was quite a bit better than my baseline too - showing that I'd been struggling a bit before the test anyway!
Once they'd made sure everything was back to normal and I was ok I was sent off on my way. I didn't feel any residual symptoms, I was just tired out from doing a lot of spirometry! So I'd advise planning a quiet day afterwards!
Needless to say my test was pretty positive and although it was uncomfortable I'm really glad I got it done as it really helped to understand my asthma a bit more and made them take me a bit more seriously when I came in unwell.
I hope this has helped explain what happens to people and I'm happy to answer any questions people might have.
Here are a couple of links for some more info on the test:
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