A 62-year-old male smoker with a 40 pack-year history presents with progressive dyspnea, chronic cough, and sputum production for 5 years. Clinical examination reveals barrel chest, pursed-lip breathing, and reduced breath sounds bilaterally. Which investigation is most appropriate to confirm the diagnosis and assess the severity of airflow obstruction?

## Investigation of Choice in COPD Diagnosis ### Why Spirometry with Bronchodilator Response? **Key Point:** Spirometry is the gold standard investigation for diagnosing and grading the severity of COPD. It objectively measures airflow obstruction and is essential for diagnosis confirmation. **High-Yield:** The diagnostic criterion for COPD is a post-bronchodilator FEV₁/FVC ratio < 0.70, as per GOLD criteria. This distinguishes COPD from other obstructive diseases and confirms irreversible airflow obstruction. ### Spirometry Parameters in COPD | Parameter | Finding in COPD | Clinical Significance | |-----------|-----------------|----------------------| | FEV₁/FVC ratio | < 0.70 (post-BD) | Diagnostic hallmark | | FEV₁ | Reduced | Severity grading | | FVC | Normal or reduced | Emphysema component | | TLC | Increased | Air trapping | | RV | Increased | Hyperinflation | **Clinical Pearl:** Bronchodilator response (BD) testing with a short-acting beta-2 agonist helps distinguish COPD (minimal BD response, <12% and <200 mL improvement) from asthma (significant BD response). ### Severity Classification (GOLD) 1. **GOLD 1 (Mild):** FEV₁ ≥ 80% predicted 2. **GOLD 2 (Moderate):** FEV₁ 50–79% predicted 3. **GOLD 3 (Severe):** FEV₁ 30–49% predicted 4. **GOLD 4 (Very Severe):** FEV₁ < 30% predicted **Tip:** Always perform spirometry before and after bronchodilator administration to assess reversibility and confirm the diagnosis.