## Investigation of Choice: Spirometry with Bronchodilator Response **Key Point:** Spirometry is the gold standard investigation for diagnosing and grading the severity of chronic obstructive pulmonary disease (COPD). The addition of bronchodilator response testing helps differentiate COPD from asthma and assess reversibility of airflow obstruction. **High-Yield:** In COPD, spirometry typically shows: - FEV₁/FVC ratio < 0.70 (diagnostic criterion) - Reduced FEV₁ (forced expiratory volume in 1 second) - Reduced FVC (forced vital capacity) or normal FVC - Minimal bronchodilator response (< 12% and < 200 mL improvement in FEV₁) **Clinical Pearl:** The FEV₁/FVC ratio of < 0.70 post-bronchodilator is the GOLD STANDARD diagnostic criterion for COPD according to GOLD guidelines. This distinguishes COPD from restrictive lung disease. **Mnemonic: COPD Spirometry Pattern** — **FRED** - **F**EV₁/FVC < 0.70 (Fixed obstruction) - **R**educed FEV₁ - **E**xpiratory flow limitation - **D**iminished bronchodilator response ### Why Spirometry is Superior in This Case The clinical presentation (smoking history, dyspnea, hyperinflation on CXR) strongly suggests COPD. Spirometry provides: 1. Objective quantification of airflow obstruction 2. Severity grading (GOLD stages 1–4 based on FEV₁ % predicted) 3. Baseline for monitoring disease progression 4. Assessment of reversibility to guide therapy ### Role of Other Investigations | Investigation | Role in COPD | Timing | |---|---|---| | Spirometry | Diagnostic & severity grading | **First-line** | | HRCT | Assess emphysema pattern, rule out other lung disease | Secondary (not routine) | | ABG | Assess hypoxemia/hypercapnia | When respiratory failure suspected | | DLCO | Assess emphysema burden | Supplementary, not diagnostic | [cite:Harrison 21e Ch 308]
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