Unclear Proportions: Blurred Lines Between Mild, Moderate and Severe Asthma Statistics

While working on an article recently, I wanted to include a statistic about the proportional representations of intermittent, mild, moderate and severe asthma. Feeling certain I had seen such a statistic somewhere for more than severe asthma, I dug into the internet.

What I found

To find… nothing really helpful. I re-found that 10-15% of asthmatics are severe, which I knew. I found that 70% of people have allergic asthma, which I knew. But I could not find of the remaining 85 to 90% of asthmatics who do not have severe asthma, what the proportions of severity are among them.

I was chatting with John at the time, so I sent him a message asking if he had a source. Of course, the nerds we are, we became somewhat insatiably curious, and I picture both of us sitting at our computers, 1111 miles from each other (according to Google Maps!), digging through the internet swearing this was a document we’d read, determined to find this answer.

Alas, such an answer was not to be had, despite throwing 5 links back and forth to each other. The closest thing I found was a UK study where patients self-assessed their asthma severity based on the Global Initiative for Asthma Guidelines, to which I said to John, “And we all know nobody accurately assesses their asthma severity.”

However, John did find an answer as to why we might not have an answer…

Why we can’t figure out proportions of asthma severity

In our inability to find the answer to our true question, John found a thread on Research Gate of researchers discussing the (lack of) answer to this question.

The first answer in the thread I thought held promise until I realized the dude had not just transposed his numbers while typing. This 2012 study suggests according to physician opinion that 46.3% of asthmatics had moderate disease, 2.4% had mild disease, and 51.3% had mild asthma.¹ I feel these opinions are not held in fact, given we have well established understanding that 10-15% of asthmatics have severe persistent disease, not 50%—it even says 15% are documented have severe asthma earlier in the article! ¹

So, from this we’ve learned that perhaps physicians are no better at assessing asthma control based on opinion than patients are—which is not to say that with the guidelines in front of them and additional data or testing, they would not make the correct assessment, I presume most would!

How we determine asthma severity

This same poster, Willmore Wesley of the University of Massachusetts at Amherst raises the important point that we do not have a more definitive answer because each study categorizes severity differently. ² While there are clear-ish guidelines for assessing asthma severity, it is true that different scientific bodies produce different guidelines on how to differentiate asthma severity among patients.

For instance, when I was diagnosed in 2008, I most commonly found severity assessed as by FEV1 and a few other factors. Now, over a decade later, there is much more nuance considered such as medications required, response to treatment, disruption to daily life, the requirement of oral corticosteroids or high dose inhaled steroids, and so forth. Many physicians use a combination of these methods when gauging a patient’s asthma severity. These may also look different in clinical practice assessment vs assessment for a clinical trial or research study (where, for instance, FEV1 values may be of more importance for measurement of the effectiveness of intervention), even though—clearly—patients deserve more consistency than this!

Mysteries to solve

We may never know what approximations of people have mild, moderate or severe asthma—and even if we did, these classifications could change, especially as we find more targeted biologic treatments that can improve quality of life for many severe asthmatics. It is also true that asthma severity can change over time, making lines blur further.

Regardless of asthma severity, more options in traditional inhaled asthma therapy may also positively impact the quality of life for asthmatics who have both severe and less severe asthma, decreasing the overall severity of asthma by more effective or improved response to treatment. While there have been few—if any—true inhaled “wonder drugs” for the rest of us for decades, I’d like to hope those mysteries to better asthma control will be in our hands soon, too. But it may be wishful thinking.

Apparently just like finding a “real answer” to my question was!