How is the severity of bronchial asthma classified and what are the corresponding treatments?

Classification of Bronchial Asthma Severity

Asthma severity is 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 frequency), with the final classification determined by the most severe category in which any feature occurs. 1, 2, 3

The Two-Domain Assessment Framework

Severity classification requires systematic evaluation of both domains before initiating therapy:

Domain 1: Impairment Assessment

Evaluate the patient's status over the previous 2-4 weeks using these specific parameters 1, 4:

• Daytime symptoms frequency: How many days per week does the patient experience asthma symptoms? 1, 3
• Nighttime awakenings: How many times per month or week does asthma wake the patient? 1, 3
• Short-acting β2-agonist use: How many days per week is rescue medication needed (excluding pre-exercise prophylaxis)? 1, 3
• Activity limitation: Does asthma interfere with normal daily activities, and to what degree? 1, 3
• Spirometry measurements: FEV1 percent predicted and FEV1/FVC ratio are mandatory for patients ≥5 years old 2, 4

Domain 2: Risk Assessment

The primary risk marker is exacerbation history 1, 4:

• Count exacerbations requiring oral systemic corticosteroids in the past year 1, 2, 3
• Patients with ≥2 exacerbations requiring oral corticosteroids annually must be classified as having persistent asthma, even if all impairment parameters suggest intermittent disease 1, 2, 3

The Four Severity Categories

Intermittent Asthma

• Symptoms ≤2 days/week 1, 3
• Nighttime awakenings ≤2 times/month 1, 3
• Short-acting β2-agonist use ≤2 days/week 1, 3
• No interference with normal activity 1, 3
• FEV1 >80% predicted with normal FEV1/FVC ratio 1, 2, 3
• 0-1 exacerbations requiring oral corticosteroids per year 1, 3

Mild Persistent Asthma

• Symptoms >2 days/week but not daily 1, 3
• Nighttime awakenings 3-4 times/month 1, 3
• Short-acting β2-agonist use >2 days/week but not daily 1, 3
• Minor limitation of normal activity 1, 3
• FEV1 >80% predicted but FEV1/FVC reduced >5% from normal 1, 2, 3
• ≥2 exacerbations requiring oral corticosteroids per year 3

Moderate Persistent Asthma

• Daily symptoms 1, 3
• Nighttime awakenings >1 time/week but not nightly 1, 3
• Daily short-acting β2-agonist use 1, 3
• Some limitation of normal activity 1, 3
• FEV1 60-80% predicted with FEV1/FVC reduced >5% 1, 2, 3
• ≥2 exacerbations requiring oral corticosteroids per year 1, 3

Severe Persistent Asthma

• Symptoms throughout the day 1, 3
• Nighttime awakenings often 7 times/week 1, 3
• Short-acting β2-agonist use several times per day 1, 3
• Extremely limited normal activity 1, 3
• FEV1 <60% predicted with reduced FEV1/FVC ratio 1, 2, 3
• ≥2 exacerbations requiring oral corticosteroids per year 1, 3

Age-Adjusted Normal FEV1/FVC Ratios

Use these age-specific cutoffs to determine if FEV1/FVC is normal or reduced 1, 2:

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

Critical Classification Rules

Assign severity to the most severe category in which ANY feature occurs across either domain 1, 4. For example, if a patient has symptoms only 3 days/week (suggesting mild persistent) but FEV1 is 55% predicted (indicating severe persistent), classify as severe persistent asthma 1, 4.

The exacerbation rule overrides impairment classification: Any patient requiring ≥2 courses of oral corticosteroids in the past year has persistent asthma and requires controller therapy, regardless of how mild their day-to-day symptoms or lung function appear 1, 2, 3.

Common Pitfalls to Avoid

• Never classify severity during an acute exacerbation, as this overestimates baseline severity and leads to overtreatment 3
• Never rely on symptoms alone without spirometry, as patients and physicians consistently underestimate severity, leading to undertreatment 1, 3
• Never ignore exacerbation history when lung function appears normal, as frequent exacerbations requiring oral corticosteroids mandate persistent asthma treatment 1, 2, 3
• Never use fixed FEV1/FVC cutoffs across all ages, as this misclassifies older patients who have age-appropriate lower ratios 1, 2, 3
• Never continue using severity classification once treatment begins—shift to control-based assessment (well controlled, not well controlled, very poorly controlled) for all subsequent treatment adjustments 1, 3, 5

Corresponding Initial Treatment by Severity

Intermittent Asthma

• Short-acting β2-agonist as needed only 3

Mild Persistent Asthma

• Low-dose inhaled corticosteroids (preferred, as they are the most effective single controller medication) 1, 3
• Alternative: leukotriene modifiers or theophylline 3

Moderate Persistent Asthma

• Low-to-medium dose inhaled corticosteroids plus long-acting β2-agonist (preferred) 3
• Alternative: medium-dose inhaled corticosteroids alone, or low-to-medium dose inhaled corticosteroids plus leukotriene modifier 3

Severe Persistent Asthma

• Medium-to-high dose inhaled corticosteroids plus long-acting β2-agonist 3
• Consider omalizumab for allergic asthma 3
• May require oral corticosteroids 3

All patients at every severity level must receive a prescription for short-acting β2-agonist rescue medication with instructions for appropriate use 1.