How do you differentiate between asthma and Chronic Obstructive Pulmonary Disease (COPD)?

Differentiating Asthma from COPD

Use post-bronchodilator spirometry as the primary diagnostic tool: asthma shows significant reversibility (≥12% and ≥200 mL improvement in FEV1), while COPD demonstrates persistent airflow obstruction (FEV1/FVC <0.70) with minimal reversibility (<10% predicted or <12% and <200 mL change). 1, 2

Diagnostic Algorithm

Step 1: Clinical History Assessment

Age and onset patterns:

• Asthma typically begins in childhood or adolescence, though adult-onset occurs; COPD predominantly develops after age 40 in patients with significant exposure history 1, 3, 4
• COPD requires substantial smoking history (≥10 pack-years) or occupational/biomass smoke exposures 2, 5

Symptom characteristics:

• Asthma: Episodic, variable symptoms including paroxysmal dyspnea, nocturnal cough (often dry), recurrent wheeze, chest tightness that worsens with triggers (exercise, allergens, cold air, viral infections, strong emotions) 1
• COPD: Progressive, persistent symptoms with dyspnea during physical exertion in early stages, progressing to rest dyspnea; productive cough is more common 3, 4

Associated features:

• Asthma: History of atopy, allergic conditions (eczema, allergic rhinitis), family history of asthma, elevated total IgE 1, 2
• COPD: Smoking history, occupational exposures, minimal atopic features 3, 2

Step 2: Spirometry Testing (Essential for Diagnosis)

Pre-bronchodilator spirometry:

• Use to rule out COPD if FEV1/FVC ≥0.7 1
• Both conditions may show airflow obstruction at baseline 1, 5

Post-bronchodilator spirometry (definitive test):

• Asthma diagnosis: FEV1 improvement >12% AND >200 mL (some evidence suggests >10% predicted may have higher discriminative value) 1, 2, 5
• COPD diagnosis: Post-bronchodilator FEV1/FVC <0.70 with minimal reversibility (<12% and <200 mL) 1, 2, 5
• The 2025 GOLD guidelines recommend using post-bronchodilator measurements to confirm COPD diagnosis, as this captures "volume responders" who may have preserved ratios pre-bronchodilator due to gas trapping 1

Important caveat: Bronchodilator responsiveness alone has poor discriminative properties and is not reproducible; it should not be used as the sole differentiating feature 1

Step 3: Additional Diagnostic Features When Available

For asthma:

• Peak flow variability >15% over 2 weeks 2
• Positive methacholine challenge (≥20% reduction in FEV1) 5
• Fractional exhaled nitric oxide (FeNO) ≥45-50 ppb 1
• Sputum eosinophilia ≥3% 1

For COPD:

• Evidence of emphysema on chest imaging 3
• Decreased diffusing capacity 3
• Persistent airflow limitation despite optimal bronchodilator therapy 2

Step 4: Recognizing Asthma-COPD Overlap

When patients display features of both conditions, consider asthma-COPD overlap if:

• Similar number of asthma and COPD features are present 1
• Spirometry shows reversibility (consistent with asthma) AND persistent baseline airflow limitation (characteristic of COPD) 5

Major criteria (Spanish/Czech guidelines):

• Strong bronchodilator response (FEV1 ≥15% and ≥400 mL) 1
• Sputum eosinophilia 1
• History of asthma 1
• FeNO ≥45-50 ppb 1

Minor criteria:

• Mild bronchodilator response (FEV1 >12% and >200 mL) 1
• Elevated total IgE 1
• History of atopy 1

Diagnosis requires: Two major criteria OR one major plus two minor criteria 1

Key Diagnostic Pitfalls to Avoid

Do not rely on clinical features alone: Cough and wheezing occur in both conditions and are not definitive without spirometry 1, 6

Beware of age-related spirometry interpretation: A fixed FEV1/FVC <0.70 cutoff may lead to COPD overdiagnosis in elderly patients 7

Recognize that bronchodilator responsiveness is unreliable: BDR is not reproducible, does not predict ICS responsiveness in COPD, and represents "phenotype mimicry" rather than true asthma features 1

Consider FEV1/SVC ratio in obese patients <60 years: If FEV1/FVC is preserved but clinical suspicion is high, FEV1/slow vital capacity ratio may detect peripheral airflow obstruction 1

Treatment Implications Based on Diagnosis

Confirmed asthma:

• First-line: Inhaled corticosteroids (ICS) as controller medication 3, 2
• Add long-acting beta-agonist (LABA) if symptoms persist 3, 2

Confirmed COPD:

• First-line: Long-acting muscarinic antagonist (LAMA) or LABA monotherapy 3, 2
• Add ICS only for frequent exacerbations, eosinophilia, or overlap features 3, 2

Asthma-COPD overlap:

• Initiate ICS/LABA combination therapy as first-line treatment 1, 3, 2
• Add LAMA for triple therapy if symptoms persist 1, 3