Asthma classifications: Severity model

So, now that we’ve discussed a bit about what asthma is, how it works, and what it looks like, why don’t I explain how asthma is classified? You’ve seen me toss around terms like “mild intermittent” “moderate” and “severe” here, but what do those terms mean? How do we classify asthma?

Well, there’s two ways: a severity model, which I’ll discuss today, and a phenotype + severity model, which I will discuss in a later post. The severity model has been used for decades, although how we classify people into each category has been refined as technology – and especially treatment – improves. There are four main categories of asthma severity:

  • Mild intermittent
  • Mild persistent
  • Moderate
  • Severe

And some more recent classification schemes include a fifth category either below or above the current severe category as “severe” encompasses too wide a range of severity to really be useful now that treatment has improved, so the fifth category was introduced to provide a more useful classification. The Canadian guidelines use “very severe,” which as it sounds is more severe than severe asthma. Under these recent Canadian guidelines, I’m classified as a severe asthmatic, but internationally, I’d be more likely to be classified as a moderate asthmatic, so that’s what I tend to use on the blog, lest I give people the wrong impression.

With the severity model, it is important to remember that doctors pick the most severe category you fit at least one criterion of. This is to prevent under-estimating a person’s severity and under-treating them (something that happened to me back when my asthma was starting to get bad again). So when you’re reading the descriptions of severity categories, remember that any one of the things I list put you in the next category up. Or, as my doctor says, “You take the worst of pulmonary function, symptoms, and medication needs, and that’s your severity.” Another important thing is that symptoms listed are what your symptoms are like without any treatment. So if you were off meds entirely, this is how bad your asthma would be. For simplicity, I’ll use the common international classifications in this post, but you can look up your country’s classification scheme if you’re curious – most countries I’ve searched post them online.

Mild intermittent asthma is defined as asthma where people experience symptoms no more than twice a week, wake up no more than twice a month, need their quick-relief puffer no more than twice a week, don’t have asthma interfere with daily activities at all peak flow and pulmonary function are normal between attacks, and asthma flares only rarely (<1/yr) require oral steroids. People with mild intermittent asthma can go weeks, months, or even years between significant flareups. Mild intermittent asthmatics need only a rescue inhaler to achieve good control.

Mild persistent asthma happens when people experience symptoms more than twice a week but not daily, or wake up 3-4 times a month, or use their quick-relief inhaler more than twice a week but not daily, or have minor limitations of daily activities without treatment or have peak flow readings of 80-100% between fares, or need oral steroids 2+ times a year. Mild persistent asthmatics are able to achieve good control, but need daily maintenance therapy, usually with low- to moderate-doses of inhaled corticosteroids.

Moderate persistent asthma happens when someone has daily symptoms, or wakes up more than once a week, or needs their quick relief puffer daily, or has some limitations of daily activity, or has peak flow of 60-80%, or peak flow variability of 15-30%, or asthma flares need oral steroids twice a year. Moderate persistent asthmatics are able to achieve good control, and are treated with high-dose corticosteroids, with or without other treatment.

Severe persistent asthma happens when someone has symptoms all day, or wake up every night, or need their inhaler several times a day, or limits activities daily, or have peak flow of <60%, or have peak flow variability of >30%, or need steroids for asthma several times a year. Severe asthmatics may or may not be able to achieve good control, always need other treatment in addition to high-dose corticosteroids. Many severe asthmatics need daily oral steroids.

Because it’s dangerous to take someone off their meds to see how bad their asthma is, in Canada, we’ve started categorizing severity based on how much meds you need to achieve control and whether or not you’re able to achieve textbook control.

The previous post in this series may be found here.
The next post in this series may be found here.