What is the interpretation of spirometry showing a Forced expiratory volume in one second/Forced vital capacity ratio of 52%, FEV1 at 51% of predicted, and FVC at 73% of predicted, and what are the recommended next steps?

Moderate-to-Severe Obstructive Lung Disease with Mixed Pattern

These spirometry values indicate moderate-to-severe obstructive lung disease with a mixed obstructive-restrictive pattern, and you should immediately perform post-bronchodilator spirometry to assess reversibility and guide diagnosis between COPD and asthma 1, 2.

Spirometry Interpretation

Your patient's values show:

• FEV1/FVC ratio of 52% (normal >70%): Confirms airflow obstruction 1, 2
• FEV1 51% predicted: Indicates moderate-to-severe obstruction 2
• FVC 73% predicted: Below 80%, suggesting a concomitant restrictive component or gas trapping 2

This is a mixed pattern - the reduced FVC alongside the obstructive ratio suggests either:

1. True restrictive disease coexisting with obstruction
2. Air trapping and hyperinflation (common in severe COPD) causing premature airway closure during forced expiration 1
3. Small airway collapse reducing the measured FVC 1

Critical Next Step: Bronchodilator Testing

You must perform post-bronchodilator spirometry before making any definitive diagnosis 1, 3. This is non-negotiable because:

• Reversibility criteria for asthma: Improvement of FEV1 or FVC by ≥12% AND ≥200 mL in adults indicates significant reversibility, suggesting asthma rather than COPD 2, 3
• The GOLD 2025 guidelines emphasize that COPD diagnosis requires post-bronchodilator FEV1/FVC <0.70 1
• Pre-bronchodilator values alone have 100% sensitivity but only 38% specificity for COPD - meaning you'll miss asthma diagnoses 3

What to Look For Post-Bronchodilator:

Volume responders (FVC improvement ≥330 mL) typically have:

• Greater baseline gas trapping
• Lower baseline FEV1 and FVC
• Higher residual volume
• More severe COPD 1

Flow responders (FEV1 improvement ≥160 mL) are more common in:

• Milder obstruction
• Asthma
• GOLD grade 2 COPD 1

Consider Slow Vital Capacity

If post-bronchodilator FEV1/FVC remains >0.70 but clinical suspicion for obstructive disease is high (especially in patients <60 years old or obese), measure slow vital capacity (SVC) 1. The FEV1/SVC ratio is more sensitive for detecting mild peripheral airflow obstruction, though less specific 1. The GOLD 2025 guidelines recommend this when there's strong clinical suspicion despite normal FEV1/FVC 1.

Additional Testing to Order

Beyond bronchodilator testing, obtain:

1. Full pulmonary function tests with lung volumes: Measure total lung capacity (TLC) and residual volume (RV) to distinguish true restriction (low TLC) from pseudorestriction due to air trapping (high RV/TLC ratio) 1, 4

2. Diffusing capacity (DLCO): Helps differentiate COPD (typically reduced) from asthma (typically normal) and identifies emphysema 4

3. Impulse oscillometry (IOS) if available: Shows increasingly abnormal values correlating with obstruction severity 4

Severity Classification

If this is COPD (post-bronchodilator FEV1/FVC <0.70 with <12% reversibility):

• FEV1 51% = GOLD Grade 2 (Moderate) if 50-79% predicted
• Or GOLD Grade 3 (Severe) if 30-49% predicted 1

The exact classification depends on whether 51% is the pre- or post-bronchodilator value.

Common Pitfall to Avoid

Do not diagnose COPD based on pre-bronchodilator spirometry alone - this leads to misdiagnosis of asthma as COPD in a substantial proportion of patients 3. The current GOLD criteria specifically require post-bronchodilator values to confirm irreversible obstruction 1.