Introduction
Asthma classification is a clinical framework used to describe how severe asthma is and how it presents in an individual. Authoritative guidelines and reviews agree that asthma is an inflammatory disease of the airways and that classifying its severity is important for guiding treatment decisions and ongoing management. Classification is based primarily on symptoms and lung function and may change over time as the disease or its response to treatment changes.
Key Takeaways
- Asthma severity is classified into four categories based on symptoms and lung function.
- Overall severity is determined by the most severe feature present.
- Asthma severity and asthma control are related but distinct concepts.
- Asthma may also be described by types related to triggers or clinical patterns.
- Classification can change over time as asthma responds to treatment.
What Asthma Classification Means
Asthma classification refers to evaluating the severity of asthma at the time of assessment, typically before long-term treatment is started. Established guidelines classify asthma using patterns of symptoms (daytime and nighttime) and objective measures of lung function. Overall severity is determined by the most severe feature present, even if other features are milder. Classification may change over time.
Asthma Severity vs. Asthma Control
Asthma severity and asthma control are related but distinct concepts:
- Asthma severity describes the underlying intensity of the disease before long-term treatment.
- Asthma control describes how well symptoms are managed with current treatment.
Guidelines emphasize that severity can change over months or years, especially as asthma responds to therapy, and that control is assessed separately using symptom patterns and lung function while on treatment.
The Four Severity Categories of Asthma
Authoritative guidelines consistently describe four severity categories based on symptoms and lung function. Patients are assigned to the category corresponding to their most severe feature.
Intermittent Asthma
- Symptoms occur infrequently.
- Nighttime symptoms occur no more than twice per month.
- Daily activities are not limited.
- Lung function is normal between attacks (generally ≥80% of expected values with minimal variability).
Mild Persistent Asthma
- Symptoms occur more than twice per week but not daily.
- Nighttime symptoms occur several times per month.
- Attacks may interfere with daily activities.
- Lung function is generally normal between attacks (≥80% of expected values).
Moderate Persistent Asthma
- Symptoms occur daily.
- Nighttime symptoms occur more than once per week.
- Symptoms interfere with daily activities.
- Short-acting asthma medication is used daily.
- Lung function shows moderate impairment (approximately 60–80% of expected values with increased variability).
Severe Persistent Asthma
- Symptoms occur throughout the day.
- Nighttime symptoms are frequent, sometimes nightly.
- Daily physical activities are severely limited.
- Lung function is substantially reduced (≤60% of expected values with high variability).
Severity Comparison Overview
| Severity Category | Symptom Pattern | Nighttime Symptoms | Activity Limitation | Lung Function |
| Intermittent | Infrequent | ≤2/month | None | Normal |
| Mild Persistent | >2/week | Several/month | Possible | Normal |
| Moderate Persistent | Daily | >1/week | Yes | Moderately reduced |
| Severe Persistent | Throughout day | Frequent | Severe | Substantially reduced |
How Severity Is Determined
Clinicians commonly use structured criteria or tables that compare:
- Daytime symptom frequency
- Nighttime symptoms
- Impact on activities
- Lung function measurements (such as spirometry or peak expiratory flow)
Overall severity is determined by the worst applicable category.
Types of Asthma
In addition to severity categories, asthma is often described by types, which relate to triggers or clinical patterns rather than baseline severity.
Examples of Asthma Types
- Allergic asthma
- Aspirin-induced asthma
- Cough-variant asthma
- Exercise-induced asthma
- Nighttime asthma
- Steroid-resistant asthma
- Occupational asthma
These types describe how asthma presents or what triggers symptoms; they do not replace severity classification.
Exercise-Induced Asthma
Some people experience asthma symptoms—such as shortness of breath, chest tightness, wheezing, or coughing—primarily during or after physical activity. This pattern is commonly referred to as exercise-induced asthma or exercise-induced bronchoconstriction.
Asthma–COPD Overlap
Some adults have features of both asthma and chronic obstructive pulmonary disease (COPD). This overlap is recognized clinically to help select the most appropriate treatment approach.
Common Symptoms of Asthma
Verified common symptoms include:
- Wheezing
- Shortness of breath
- Chest tightness
- Coughing, including nighttime coughing
Symptom patterns are central to assessing both severity and control.
Causes and Disease Features
Asthma is a chronic inflammatory disease of the airways characterized by airway narrowing. High-quality sources confirm inflammation and variable airflow limitation as defining features.
For other proposed causes or risk factors, there is no high-quality evidence supporting specific claims within the verified source set.
How Asthma Is Diagnosed
Lung Function Testing
- Spirometry measures lung function, including forced expiratory volume in one second (FEV₁).
- Peak expiratory flow (PEF) may be used to assess lung function and monitor changes over time.
Multiple tests may be used; no single test is sufficient in all cases.
Claims about diagnosis based on treatment response or allergy testing lack high-quality evidence within the verified sources.
Asthma in Young Children
Asthma in children younger than four years can be difficult to diagnose. Symptoms and presentation may differ from those in older children and adults.
Specific diagnostic methods beyond this are not supported by high-quality evidence in the verified sources.
Treatment Overview
High-quality sources confirm that:
- Treatment commonly includes anti-inflammatory medications, such as inhaled corticosteroids.
- Bronchodilators relieve bronchospasm but do not treat underlying inflammation.
- Management strategies are guided by severity classification and assessments of asthma control.
When to See a Doctor
Based on verified evidence:
- Ongoing assessment and follow-up with a healthcare professional are important for monitoring asthma severity and control.
- Patients are advised to take medications as prescribed and report how well treatment controls symptoms during follow-up visits.
Specific emergency warning signs or thresholds for urgent care are not supported by high-quality evidence within the verified source set.
Frequently Asked Questions
What are the four categories of asthma?
Intermittent, mild persistent, moderate persistent, and severe persistent asthma.
How is asthma classified?
Asthma is classified using symptom patterns (daytime and nighttime) and lung function measurements, with overall severity determined by the most severe feature present.
Are asthma severity and asthma control the same?
No. Severity reflects underlying disease intensity before treatment, while control describes how well symptoms are managed with current treatment.
Are there different types of asthma?
Yes. Asthma may also be described by types such as allergic, exercise-induced, or occupational asthma, which relate to triggers or clinical patterns rather than severity.
How many types of asthma are there?
There is no high-quality evidence supporting a single number of asthma types.
What are the stages or levels of asthma?
High-quality evidence supports four severity categories, not stages.
What is mild asthma?
Mild asthma generally refers to intermittent or mild persistent asthma as defined by symptom frequency and lung function.
What is moderate asthma?
Moderate asthma corresponds to moderate persistent asthma, characterized by daily symptoms, regular nighttime symptoms, and moderate lung function impairment.
What is severe asthma?
Severe asthma corresponds to severe persistent asthma, with frequent day and night symptoms, significant activity limitation, and markedly reduced lung function.
APA Reference List
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Centers for Disease Control and Prevention. (2024, January 22). About asthma. https://www.cdc.gov/asthma/about/index.html
Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health. (2024, January 2). About work-related asthma. https://www.cdc.gov/niosh/asthma/about/index.html
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National Asthma Education and Prevention Program, National Heart, Lung, and Blood Institute. (2012, September). Asthma care quick reference: Diagnosing and managing asthma (NIH Publication No. 12-5075). https://www.nhlbi.nih.gov/files/docs/guidelines/asthma_qrg.pdf
World Health Organization. (2024, May 6). Asthma (Fact sheet). https://www.who.int/news-room/fact-sheets/detail/asthma