Which test confirms a COPD diagnosis with spirometry?

• A. Chest X-ray showing hyperinflation
• B. Arterial blood gas with PaO2 > 100
• C. CT scan with ground-glass opacities
• D. Spirometry showing FEV1/FVC ratio < 70%

Answer: (D)

Spirometry is the test that directly measures how well the airways are flowing and whether the obstruction is persistent. In COPD, the hallmark is airflow limitation that remains after using a bronchodilator. The key finding is a post-bronchodilator FEV1/FVC ratio less than 0.70, which shows that the airways remain narrowed despite relaxation of smooth muscle. FEV1 is the amount of air forced out in the first second, and FVC is the total air exhaled; when the ratio is reduced, it indicates obstructive airflow limitation consistent with COPD. This objective, reproducible measurement is what confirms the diagnosis rather than imaging or gas exchange values alone.

Imaging like chest X-ray can show hyperinflation or other changes that might accompany COPD but they don’t quantify airway obstruction or confirm its persistence. An arterial blood gas with a high PaO2 does not diagnose COPD—it reflects gas exchange status and isn’t about airway mechanics. A CT scan with ground-glass opacities points to other processes such as infection or interstitial disease, not the chronic airflow limitation seen in COPD. So the spirometry result showing a FEV1/FVC ratio below 0.70 best confirms COPD.