A 62-year-old man with a 40 pack-year smoking history presents with progressive dyspnea, chronic cough, and sputum production for 3 years. Clinical examination reveals barrel chest, pursed-lip breathing, and reduced breath sounds bilaterally. Which investigation is most appropriate to confirm the diagnosis of COPD and assess disease severity?

Explanation

## Diagnosis and Confirmation of COPD **Key Point:** Spirometry is the gold standard and investigation of choice for confirming COPD diagnosis and assessing disease severity. It provides objective measurement of airflow obstruction. ### Why Spirometry Is Diagnostic Spirometry with bronchodilator response establishes: 1. **Airflow obstruction:** FEV₁/FVC ratio <0.70 (post-bronchodilator) confirms persistent airflow limitation 2. **Severity grading:** Based on FEV₁ % predicted: - GOLD 1 (Mild): FEV₁ ≥80% predicted - GOLD 2 (Moderate): 50–79% predicted - GOLD 3 (Severe): 30–49% predicted - GOLD 4 (Very Severe): <30% predicted 3. **Reversibility assessment:** <12% and <200 mL improvement post-bronchodilator excludes asthma **High-Yield:** The FEV₁/FVC ratio <0.70 post-bronchodilator is the diagnostic criterion for COPD per GOLD guidelines. This distinguishes COPD from asthma (which shows reversibility). ### Role of Other Investigations | Investigation | Role in COPD | |---|---| | Chest X-ray | Screens for alternative diagnoses (pneumonia, TB, malignancy); not diagnostic for COPD | | HRCT thorax | Reserved for atypical presentations, suspected bronchiectasis, or emphysema phenotyping | | ABG analysis | Assesses oxygenation/CO₂ retention in advanced disease; not diagnostic | **Clinical Pearl:** A patient with clinical features of COPD (smoking history, dyspnea, cough) but normal spirometry does NOT have COPD—spirometry is mandatory before diagnosis. [cite:Harrison 21e Ch 297]