## Investigation of Choice for COPD Diagnosis and Severity Assessment **Key Point:** Spirometry is the gold standard and investigation of choice for diagnosis and grading of COPD severity. It objectively measures airflow obstruction and is essential for all patients with suspected COPD. ### Spirometry Parameters in COPD | Parameter | Normal | COPD Finding | |-----------|--------|-------------| | FEV₁/FVC ratio | ≥ 0.70 | < 0.70 (diagnostic) | | FEV₁ | ≥ 80% predicted | Reduced (severity graded) | | FEF 25-75% | Normal | Reduced (small airway disease) | | Bronchodilator response | < 12% & < 200 mL | Minimal (unlike asthma) | **High-Yield:** The FEV₁/FVC ratio < 0.70 is the diagnostic hallmark of COPD and confirms persistent airflow limitation [cite:GOLD 2023]. ### COPD Severity Grading by FEV₁ 1. **GOLD 1 (Mild):** FEV₁ ≥ 80% predicted 2. **GOLD 2 (Moderate):** 50–79% predicted 3. **GOLD 3 (Severe):** 30–49% predicted 4. **GOLD 4 (Very Severe):** < 30% predicted **Clinical Pearl:** Bronchodilator response (< 12% and < 200 mL improvement) helps differentiate COPD from asthma, where reversibility is typically ≥ 12% and ≥ 200 mL. **Warning:** Do not confuse COPD with asthma based on spirometry alone — clinical history and lack of significant bronchodilator response are key distinguishing features. ### Why Spirometry is Superior to Other Tests - **Objective & reproducible:** Quantifies airflow obstruction independent of clinical impression - **Diagnostic:** Confirms diagnosis when clinical suspicion exists - **Prognostic:** FEV₁ is the strongest predictor of mortality and exacerbation risk - **Monitoring:** Tracks disease progression and response to therapy **Mnemonic:** **COPD Diagnosis = FEV₁/FVC < 0.70** — this single ratio confirms the diagnosis.
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