Alternative Asthma Classification Systems
Beyond the traditional symptom-frequency/FEV1 severity scheme, asthma should be classified using a dual-domain assessment system that evaluates both "impairment" and "risk," with additional classification based on "control" status rather than severity alone once treatment is initiated 1.
Primary Alternative Classification Framework
The Expert Panel Report 3 (EPR-3) introduced a paradigm shift from simple severity classification to a two-domain assessment system 1:
1. Impairment Domain
Measures current burden:
- Frequency and intensity of symptoms
- Functional limitations currently experienced
- Impact on quality of life and daily activities
- Current lung function status
2. Risk Domain
Assesses future threats:
- Likelihood of exacerbations
- Progressive decline in lung function
- Reduced lung growth (in children)
- Risk of medication adverse effects
Critical distinction: These two domains may respond differently to treatment. Patients can have well-controlled symptoms (low impairment) but remain at high risk for severe exacerbations, requiring treatment escalation despite apparent symptom control 1.
Control-Based Classification (Post-Treatment Initiation)
Once therapy begins, the classification emphasis shifts from severity to control 1:
- Controlled asthma
- Partly controlled asthma
- Uncontrolled asthma
This uses parameters including:
- Frequency of daytime/nighttime symptoms
- Activity limitations
- Rescue medication use
- Lung function (FEV1 or PEF)
- Exacerbation frequency
Important caveat: The 2012 and 2014 GINA control classifications show poor agreement with each other, with the 2014 criteria classifying 44% of patients as controlled versus only 10% by 2012 criteria 2. This highlights ongoing evolution and lack of standardization.
Specialized Classification Systems
Severe Asthma Subclassifications
Multiple competing definitions exist with poor agreement 2:
- WHO 2010: Distinguishes "Difficult-to-treat severe asthma" from "Treatment-resistant severe asthma"
- ATS 2000: Defines "Refractory asthma"
- ERS/ATS 2014: "Severe asthma" classification
Key finding: These show poor agreement, with only moderate concordance between ATS 2000 and ERS/ATS 2014 (Kappa 0.64). The WHO classification particularly diverges from others 2.
Phenotype-Based Classification
Emerging cluster analysis identifies 5 distinct asthma phenotypes based on age of onset, atopy, lung function, and obesity 3:
- Early-onset atopic with varying medication needs (2 clusters)
- Late-onset obese female with less atopy
- Severe obstruction with variable bronchodilator response (2 clusters)
This approach recognizes asthma as a clinical syndrome rather than single disease 3.
Practical Application Algorithm
For initial assessment (treatment-naïve patients):
- Classify severity using both impairment AND risk domains
- Identify precipitating factors and comorbidities
- Initiate treatment based on severity classification
For ongoing management (on treatment):
- Assess control status (not severity) at each visit
- Evaluate both impairment and risk domains separately
- Step up therapy if either domain inadequately controlled
- Step down only when both domains well-controlled
For severe asthma evaluation:
- Apply multiple classification systems recognizing their poor agreement
- Consider phenotypic clustering for targeted therapy selection
- Assess for difficult-to-treat versus treatment-resistant disease
Common Pitfalls
- Focusing solely on symptoms while ignoring exacerbation risk: Patients may appear well-controlled but remain at high risk 1
- Using only FEV1: This misses small airway dysfunction and doesn't correlate well with all clinical outcomes 4, 5
- Assuming severity classifications are interchangeable: Different systems (WHO, ATS, ERS/ATS) identify different patient populations 2
- Relying on single measures: Multiple parameters are needed as they assess different disease manifestations and may not correlate 1