Classification of Asthma Severity
Asthma severity should be classified into four categories—intermittent, mild persistent, moderate persistent, and severe persistent—based on a two-domain assessment of impairment (symptoms, lung function, activity limitation) and risk (exacerbation history), with the final classification determined by the most severe category in which any feature occurs. 1, 2
The Four Severity Categories
Intermittent Asthma
- Symptoms: ≤2 days per week 1, 3
- Nighttime awakenings: ≤2 times per month 1, 3
- SABA use: ≤2 days per week 1
- Activity limitation: None 1
- Lung function: FEV₁ ≥80% predicted with normal FEV₁/FVC ratio 1, 2
- Exacerbations: 0-1 per year requiring oral corticosteroids 1, 3
Mild Persistent Asthma
- Symptoms: >2 days per week but not daily 1, 3
- Nighttime awakenings: 3-4 times per month 1, 3
- SABA use: >2 days per week but not more than once daily 1
- Activity limitation: Minor 1
- Lung function: FEV₁ ≥80% predicted but FEV₁/FVC reduced >5% from normal 1, 2
- Exacerbations: ≥2 per year requiring oral corticosteroids 1, 3
Moderate Persistent Asthma
- Symptoms: Daily 1, 3
- Nighttime awakenings: >1 time per week but not nightly 1, 3
- SABA use: Daily 1
- Activity limitation: Some limitation 1, 3
- Lung function: FEV₁ 60-80% predicted with FEV₁/FVC reduced >5% 1, 2
- Exacerbations: ≥2 per year requiring oral corticosteroids 1
Severe Persistent Asthma
- Symptoms: Throughout the day 1, 3
- Nighttime awakenings: Often 7 times per week 1, 3
- SABA use: Several times per day 1
- Activity limitation: Extremely limited 1, 3
- Lung function: FEV₁ <60% predicted 1, 2, 3
- Exacerbations: ≥2 per year requiring oral corticosteroids 1
Critical Classification Principles
Two-Domain Assessment
- Impairment domain includes daytime symptoms, nighttime awakenings, SABA use, activity limitation, and objective lung function (FEV₁ and FEV₁/FVC ratio) 1, 2
- Risk domain focuses on exacerbation history, specifically the number of episodes requiring oral systemic corticosteroids in the past year 1, 2
- The final severity classification is determined by the most severe category in which any single feature occurs across both domains 1, 3
Age-Adjusted FEV₁/FVC Norms
- Ages 8-19 years: Normal FEV₁/FVC = 85% 1, 2
- Ages 20-39 years: Normal FEV₁/FVC = 80% 1, 2
- Ages 40-59 years: Normal FEV₁/FVC = 75% 1, 2
- Ages 60-80 years: Normal FEV₁/FVC = 70% 1, 2
Special Exacerbation Rule
- Patients with ≥2 exacerbations requiring oral corticosteroids in the past year should be classified as having persistent asthma, even if all other parameters suggest intermittent disease. 1, 2, 3
- This rule recognizes that exacerbation history is a powerful predictor of future risk regardless of baseline lung function or symptoms 1, 2
When to Classify Severity
- Severity classification should ideally be performed BEFORE initiating controller therapy, as treatment masks the true underlying disease severity 1, 2, 3
- Once treatment begins, switch to control-based assessment (well controlled, not well controlled, very poorly controlled) for all ongoing management decisions 1, 3
- Do not attempt to classify severity during acute exacerbations, as this overestimates baseline severity and leads to overtreatment 3
Initial Treatment Based on Severity
Intermittent Asthma
- Short-acting β-agonist as needed only 3
Mild Persistent Asthma
Moderate Persistent Asthma
- Low-to-medium dose inhaled corticosteroids plus long-acting β-agonist (preferred) 3
- Alternative: medium-dose inhaled corticosteroids alone or low-to-medium dose inhaled corticosteroids plus leukotriene modifier 3
Severe Persistent Asthma
- Medium-dose inhaled corticosteroids plus long-acting β-agonist 3
- Consider omalizumab for allergic asthma 3
- High-dose inhaled corticosteroids plus long-acting β-agonist plus oral corticosteroids may be needed 3
Common Classification Pitfalls
- Never rely on symptoms alone without objective spirometry, as this leads to misclassification and undertreatment of patients with poor symptom perception 2, 3
- Never ignore exacerbation history when lung function appears normal—frequent oral corticosteroid use mandates persistent asthma treatment regardless of FEV₁ 2, 3
- Never use fixed FEV₁/FVC cutoffs across all ages—failure to apply age-adjusted norms misclassifies older patients 2, 3
- Never classify severity during acute exacerbations—wait until the patient is stable to avoid overestimating baseline severity 3
- Never continue using severity classification once treatment begins—switch to control-based assessment for all treatment adjustments 1, 3