Spirometry Interpretation: Mixed Obstructive-Restrictive Pattern
This patient has a mixed ventilatory defect with moderate obstruction and moderate restriction, requiring confirmation with full pulmonary function testing including lung volumes and DLCO, followed by initiation of long-acting bronchodilator therapy if COPD is confirmed. 1
Diagnostic Classification
Pattern Recognition
- FEV1/FVC ratio of 76%: This is above the diagnostic threshold of 70% used to define airflow obstruction 1
- However, both FEV1 (62% predicted) and FVC (65% predicted) are significantly reduced, indicating a restrictive pattern 1, 2
- The FEV1/FVC ratio >70% with reduced FVC suggests restriction rather than pure obstruction 1
Critical Caveat
This spirometry pattern does NOT meet criteria for COPD diagnosis because the post-bronchodilator FEV1/FVC ratio must be <0.70 to confirm airflow obstruction 1, 3. The ratio of 76% (0.76) is above this threshold, despite the reduced absolute values 1.
Differential Diagnosis Considerations
Most Likely Patterns
- Restrictive lung disease (interstitial lung disease, chest wall disorders, neuromuscular disease) 1, 2
- Early/mild obstruction with poor effort (requires repeat testing) 1
- Mixed defect if lung volumes confirm both restriction (low TLC) and obstruction 1, 2
Important Distinction
The reduced FVC with preserved FEV1/FVC ratio is suggestive but not diagnostic of restriction 1. A low FVC alone does not prove restrictive disease and can occur with poor effort or submaximal inspiration 1, 2.
Required Next Steps
Immediate Actions
- Confirm spirometry quality: Verify the test met acceptability criteria (grade A preferred, but even grade E can be used with clinical context) 3
- Repeat spirometry: Up to one-third of patients may shift diagnostic categories on repeat testing, particularly if baseline effort was suboptimal 4
- Obtain post-bronchodilator values if not already done: Post-BD spirometry is required to confirm any obstructive diagnosis 1, 3
Definitive Testing
Order complete pulmonary function tests including:
- Total lung capacity (TLC): TLC <5th percentile confirms true restriction 1
- DLCO measurement: Helps differentiate interstitial disease (low DLCO) from chest wall/neuromuscular causes (normal DLCO) 1
- Lung volumes (RV, FRC): Assess for air trapping or hyperinflation 1
Management Algorithm
If Restriction is Confirmed (TLC <5th percentile)
- Pursue workup for interstitial lung disease, chest wall disorders, or neuromuscular disease based on clinical context 1
- Consider high-resolution CT chest 3
- Refer to pulmonology for further evaluation 1
If Mixed Defect is Confirmed (Low TLC + FEV1/FVC <0.70 on repeat)
- Initiate long-acting bronchodilator (LAMA or LABA) as first-line therapy 5, 3
- Provide short-acting bronchodilator for rescue use 5, 3
- Address smoking cessation if applicable 1
- Schedule follow-up in 4-6 weeks to assess response, inhaler technique, and symptom control 1, 3
If Repeat Testing Shows FEV1/FVC <0.70
This would reclassify as moderate COPD (GOLD 2) based on FEV1 50-79% predicted 1, 3:
- Start long-acting bronchodilator monotherapy 5, 3
- Consider inhaled corticosteroids only if frequent exacerbations develop 5, 3
- Annual spirometry to monitor progression 3
Common Pitfalls to Avoid
Diagnostic Errors
- Do not diagnose COPD with FEV1/FVC >0.70: This is the most critical error; the ratio must be <0.70 post-bronchodilator 1, 3
- Do not assume restriction from low FVC alone: TLC measurement is mandatory to confirm restriction 1
- Do not use a single spirometry test for definitive diagnosis: Repeat testing is essential given 14-15% of patients change categories within one year 4
Age Considerations
- In patients >70 years, FEV1/FVC ratios down to 65% may be normal, and the fixed 70% threshold may overdiagnose obstruction 6, 7
- Consider using lower limit of normal (LLN) rather than fixed ratio in elderly patients 6, 7