COPD vs Asthma — Differences, PFTs, and Treatment Compared

Creator: Progress Note
Published: 2026-07-22
Keywords: COPD vs asthma, COPD asthma difference, PFT obstructive pattern, COPD treatment GOLD guidelines, asthma step therapy

The 60-second version

Asthma: reversible obstruction; COPD: irreversible, smoking-related
Both: FEV1/FVC <0.70 (obstructive); reversibility testing differentiates
COPD exacerbation: SABA + SAMA + steroids + antibiotics if purulent
O2 target in COPD: 88–92% (avoid hypercapnic drive suppression)
Alpha-1-antitrypsin deficiency: young non-smoker with lower-lobe emphysema

Pathophysiology and Patient Profile

Asthma: reversible airway obstruction from bronchospasm, mucosal edema, and mucus hypersecretion. Triggered by allergens, exercise, cold air, infections. Typically young, atopic. COPD: irreversible or minimally reversible obstruction from emphysema (alveolar destruction) and/or chronic bronchitis (productive cough >3 months/year for ≥2 years). Etiology: cigarette smoking (90%+), alpha-1-antitrypsin deficiency (young patients, lower lobe emphysema, non-smoker). Typically older (>40), current/ex-smoker.

Pulmonary Function Tests

Both show obstructive pattern: FEV1/FVC ratio <0.70. Severity of COPD by FEV1 % predicted: GOLD 1 (mild) ≥80%, GOLD 2 (moderate) 50–79%, GOLD 3 (severe) 30–49%, GOLD 4 (very severe) <30%. Reversibility testing (post-bronchodilator FEV1): Asthma = significant improvement (>12% and 200 mL increase in FEV1). COPD = minimal or no reversibility. Diffusing capacity (DLCO): low in emphysema (loss of alveolar surface area), normal or high in asthma and chronic bronchitis.

COPD Exacerbation Management

Short-acting beta-agonist (albuterol) + ipratropium (SABA + SAMA), systemic corticosteroids (prednisone 40 mg × 5 days — same outcome as 14 days), antibiotics if purulent sputum or increased dyspnea (azithromycin, amoxicillin-clavulanate, doxycycline). Controlled O2 — target SpO2 88–92% (hypercapnic patients lose hypoxic drive; excess O2 can worsen CO2 retention). BiPAP if pH <7.35.

Asthma Step Therapy

Step 1: SABA PRN (albuterol). Step 2: low-dose inhaled corticosteroid (ICS) + SABA PRN. Step 3: low-dose ICS + LABA. Step 4: medium-dose ICS + LABA. Step 5: high-dose ICS + LABA ± tiotropium. Step 6: add systemic corticosteroids. Biologic options (severe asthma): omalizumab (anti-IgE, allergic asthma), mepolizumab (anti-IL-5, eosinophilic asthma).

Test yourself

Quick check — 3 questions

1. A 62-year-old smoker has FEV1/FVC 0.58, FEV1 52% predicted, and DLCO 48% predicted. Post-bronchodilator FEV1 improves by 4%. Diagnosis?

2. A COPD patient on 4L O2 nasal cannula has SpO2 98%. The most appropriate action is:

3. A 38-year-old non-smoker develops progressive dyspnea and is found to have lower-lobe emphysema on CT. The most important diagnostic test is:

Frequently asked questions

Can a patient have both COPD and asthma?

Yes — this is called asthma-COPD overlap (ACO). Patients have features of both: smoking history with fixed airflow obstruction (COPD) plus significant reversibility or eosinophilia (asthma). ACO patients have more frequent exacerbations and worse outcomes than either disease alone. Treatment includes ICS (essential for asthma component) plus LABA/LAMA as in COPD.

Why is oxygen therapy limited to 88–92% saturation in COPD exacerbations?

Patients with severe chronic hypercapnia adapt over time by relying more on hypoxia (rather than hypercapnia) as the respiratory drive. Providing excess oxygen removes this hypoxic stimulus, causing respiratory depression and worsening CO2 retention. This 'hypoxic drive' theory is an oversimplification — the dominant mechanism is actually V/Q mismatch worsening (Haldane effect) — but the clinical practice of targeting SpO2 88–92% in COPD exacerbation is well-validated.

What spirometry result confirms a diagnosis of COPD?

Post-bronchodilator FEV1/FVC ratio <0.70 is the diagnostic threshold for COPD per GOLD guidelines. The obstruction must persist after bronchodilator administration (post-BD) to confirm fixed airway obstruction. FEV1 percent predicted is then used to classify severity (GOLD 1–4).

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