How is asthma severity determined?

How to Determine Asthma Severity

Asthma severity should be determined before initiating therapy using a two-domain assessment that evaluates both current impairment (symptoms, rescue inhaler use, activity limitation, and spirometry) and future risk (exacerbation frequency requiring oral corticosteroids), with the final classification assigned to the most severe category in which any feature occurs. 1

Classification Framework

Asthma severity is divided into four categories: intermittent, persistent-mild, persistent-moderate, and persistent-severe. 1 The term "mild-intermittent" has been eliminated from current guidelines because it fails to capture patients who experience periods of moderate or severe exacerbations. 1

Domain 1: Current Impairment Assessment

Evaluate these specific parameters over the previous 2-4 weeks: 1

Symptom Frequency

• Intermittent: ≤2 days/week 1
• Persistent-mild: >2 days/week but not daily 1
• Persistent-moderate: Daily symptoms 1
• Persistent-severe: Symptoms throughout the day 1

Nighttime Awakenings

• Intermittent: ≤2 times/month 1
• Persistent-mild: 3-4 times/month 1
• Persistent-moderate: >1 time/week but not nightly 1
• Persistent-severe: Often 7 times/week 1

Short-Acting Beta-Agonist Use for Symptom Relief

• Intermittent: ≤2 days/week 1
• Persistent-mild: >2 days/week but not more than once daily 1
• Persistent-moderate: Daily use 1
• Persistent-severe: Several times per day 1

Activity Limitation

• Intermittent: None 1
• Persistent-mild: Minor limitation 1
• Persistent-moderate: Some limitation 1
• Persistent-severe: Extremely limited 1

Spirometry (FEV₁ and FEV₁/FVC Ratio)

Spirometry is mandatory for severity classification in patients ≥5 years old. 1, 2 Physicians' subjective assessments of airway obstruction are often inaccurate, making objective measurement essential. 3

FEV₁ % Predicted: 1, 2

• Intermittent: ≥80% predicted 1, 2
• Persistent-mild: ≥80% predicted 1, 2
• Persistent-moderate: 60-80% predicted 1, 2
• Persistent-severe: <60% predicted 1, 2

FEV₁/FVC Ratio: 1, 2

• Intermittent: Normal ratio 1, 2
• Persistent-mild: Reduced >5% from normal 1, 2
• Persistent-moderate: Reduced >5% from normal 1, 2
• Persistent-severe: Reduced >5% from normal 1, 2

Age-specific normal FEV₁/FVC ratios: 1, 2

• 8-19 years: 85% 1, 2
• 20-39 years: 80% 1, 2
• 40-59 years: 75% 1, 2
• 60-80 years: 70% 1, 2

Domain 2: Future Risk Assessment

Exacerbation frequency requiring oral systemic corticosteroids is the primary marker of risk. 1

• 0-1 exacerbations per year: Lower risk 1
• ≥2 exacerbations per year: Higher risk, classify as persistent asthma regardless of impairment domain 1, 2

Critical caveat: Patients at any severity level, including intermittent asthma, can experience severe exacerbations. 1 Patients with ≥2 exacerbations requiring oral corticosteroids in the past year should be treated as having persistent asthma even if lung function and symptoms suggest intermittent disease. 1, 2

Assigning Final Severity Classification

The final severity classification is determined by the most severe category in which ANY feature of impairment or risk occurs. 1, 2 This means if a patient has daily symptoms (moderate persistent) but FEV₁ <60% (severe persistent), they are classified as severe persistent. 1

Common Pitfalls to Avoid

Do not assess severity during an acute exacerbation — severity should ideally be determined during a stable period before initiating therapy. 2 Assessing during exacerbations may overestimate baseline severity. 2

Do not rely solely on symptoms without spirometry — this leads to misclassification of severity. 2 Objective lung function measurement is essential. 1, 2

Do not ignore exacerbation history in patients with good lung function — failing to consider the risk domain may result in undertreating patients who have frequent exacerbations despite normal spirometry. 2

Do not use age-inappropriate FEV₁/FVC normal values — not accounting for age-related changes leads to misclassification. 2

Recognize that nocturnal symptoms may disproportionately drive severity classification — in large datasets, nocturnal symptoms classified the majority of patients as severe persistent, while other variables suggested milder disease, highlighting poor correlation between individual severity variables. 4

Distinction from Asthma Control

Once therapy is initiated, the emphasis shifts from assessing severity to monitoring asthma control, which guides decisions to step up or step down therapy. 1 Severity is assessed to initiate therapy; control is assessed to adjust therapy. 1