## Why COPD is right The absence of significant bronchodilator reversibility (< 12% AND < 200 mL increase in FEV1) is the hallmark spirometric finding that distinguishes COPD from asthma. Per GOLD 2024 and Harrison 21e Ch 287, significant reversibility is defined as ≥ 12% AND ≥ 200 mL increase in FEV1 or FVC post-bronchodilator; this pattern suggests asthma. In this patient, the increase of only 8% and 150 mL falls below both thresholds, making COPD the diagnosis. The obstructive pattern (FEV1/FVC < 0.7), concave expiratory limb, and reduced PEFR all support obstructive airway disease, and the lack of reversibility confirms COPD rather than asthma. ## Why each distractor is wrong - **Asthma**: Asthma typically shows significant bronchodilator reversibility (≥ 12% AND ≥ 200 mL increase in FEV1). This patient's minimal response (8%, 150 mL) argues against asthma as the primary diagnosis. - **Asthma-COPD Overlap Syndrome**: While ACOS can occur when COPD patients have partial reversibility, the degree of reversibility in this case (8%, 150 mL) is too minimal to meet criteria for overlap; true overlap requires significant reversibility superimposed on fixed obstruction. - **Restrictive lung disease with secondary airflow obstruction**: Restrictive disease would show reduced FVC with normal or elevated FEV1/FVC ratio (≥ 0.7). This patient has FEV1/FVC = 0.65 (obstructive pattern), not a restrictive pattern. **High-Yield:** Post-bronchodilator reversibility ≥ 12% AND ≥ 200 mL = asthma; < 12% or < 200 mL = COPD (lack of significant reversibility is the spirometric hallmark of COPD). [cite: Harrison 21e Ch 287; GOLD 2024]
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