Which spirometry pattern confirms an obstructive disorder?

• A. Increased FEV1/FVC ratio with reduced FVC.
• B. Normal FEV1/FVC with reduced FVC.
• C. Decreased FEV1/FVC ratio (<70%), with normal or increased FVC.
• D. Decreased FEV1/FVC ratio with reduced FVC.

Answer: (C)

Obstruction shows up on spirometry as airflow limitation where the amount you can force out in the first second drops more than the total amount you can exhale. This makes the FEV1/FVC ratio fall below the normal range (often under 70% of predicted). At the same time, the total exhaled volume (FVC) is usually normal or even increased in obstructive conditions due to air trapping and hyperinflation. So, the pattern of a decreased FEV1/FVC ratio with normal or increased FVC is characteristic of obstruction. In contrast, a normal or high ratio with reduced FVC points to a restrictive pattern, where both volumes tend to be reduced.