In spirometry, what FEV1/FVC ratio indicates obstruction, and how is severity categorized by FEV1 % predicted?

• A. FEV1/FVC < 0.70; severity: mild >80%, moderate 60–79%, moderate-severe 40–59%, severe <40%.
• B. FEV1/FVC > 0.90; severity does not relate to FEV1% predicted.
• C. FEV1/FVC < 0.80; mild >90%.
• D. FEV1/FVC < 0.60; mild >70%.

Answer: (A)

Obstruction on spirometry is indicated by a reduced FEV1/FVC ratio, reflecting decreased expiratory flow. The fixed threshold commonly used is FEV1/FVC less than 0.70, which signals obstructive physiology such as COPD or asthma with an abnormal expiratory pattern. After identifying obstruction, severity is based on how the FEV1 compares to the predicted value for the patient’s demographics. An FEV1 greater than 80% of predicted is categorized as mild; 60–79% is moderate; 40–59% is moderate-to-severe; and less than 40% is severe. It’s worth noting that some guidelines use the lower limit of normal to define obstruction, but the fixed 0.70 threshold is the standard tested here. The other options either propose incorrect ratio cutoffs or inappropriate severity ranges, which do not fit how obstruction and its severity are assessed on spirometry.