## Clinical Context The spirometric pattern described is **obstructive airflow limitation**: FEV₁/FVC < 0.70 (0.68), reduced FEV₁ (58% predicted), and a scooped-out expiratory flow-volume loop — the hallmark of COPD or asthma. ## Why Bronchodilator Reversibility Testing is the Next Step **Key Point:** Bronchodilator reversibility testing (BDRT) is the gold standard next investigation after identifying an obstructive pattern on spirometry. It distinguishes between **asthma** (reversible airflow obstruction) and **COPD** (irreversible or minimally reversible). **High-Yield:** The diagnostic criterion for reversibility is an increase in FEV₁ ≥ 12% AND ≥ 200 mL after inhalation of a short-acting β₂-agonist (salbutamol 400 µg). This finding supports asthma; absence supports COPD [cite:Harrison 21e Ch 242]. ## Interpretation Framework | Finding | Interpretation | Next Step | |---------|---|---| | Reversible obstruction (FEV₁ ↑ ≥12% & ≥200 mL) | Asthma | Initiate ICS-based therapy | | Irreversible or minimal reversal | COPD | GOLD staging; initiate bronchodilators | | Borderline reversal (8–11%) | Asthma-COPD overlap | Clinical correlation + trial of ICS | **Clinical Pearl:** In this patient, the smoking history and chronic cough suggest COPD, but BDRT is mandatory to rule out asthma or asthma-COPD overlap (ACO) before committing to long-term therapy. ## Why Not the Other Options - **HRCT chest:** Indicated only if suspicion for interstitial lung disease (ILD) exists; the obstructive pattern and smoking history point to COPD, not ILD. - **Triple therapy immediately:** Premature without phenotyping (asthma vs. COPD); BDRT guides the choice between ICS-containing vs. non-ICS regimens. - **Methacholine challenge:** Used to diagnose asthma in patients with **normal spirometry** and clinical suspicion; contraindicated in significant airflow obstruction (FEV₁ < 70% predicted) due to risk of severe bronchospasm.
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