What is the interpretation and management of abnormal PFT results showing an obstructive pattern?

PFT Interpretation: Normal Lung Function Without Obstruction

These PFT results demonstrate normal pulmonary function without any obstructive pattern. The post-bronchodilator FEV1/FVC ratio of 81% is well above the threshold for obstruction, confirming normal airway caliber 1.

Primary Spirometric Analysis

Obstruction Assessment

• FEV1/FVC ratio of 81% (108% predicted, Z-score 0.75) definitively excludes obstructive lung disease 1
• The European Respiratory Society defines obstruction as FEV1/VC below the 5th percentile of predicted values, which this patient clearly exceeds 1
• Using a fixed ratio of 0.70 would be inappropriate here, as the 5th percentile method prevents overdiagnosis of obstruction, particularly in older patients 1, 2

Volume Parameters

• FVC is 98% predicted (Z-score -0.14), which is completely normal 1
• FEV1 is 106% predicted (Z-score 0.32), which is normal to supranormal 1
• Both volumes are proportionally preserved, ruling out any restrictive process 1

Lung Volume Measurements

TLC and Compartments

• TLC at 83% predicted is at the lower end of normal but above the 5th percentile threshold for restriction 1
• A restrictive defect requires TLC below the 5th percentile with normal FEV1/VC ratio—this patient has normal FEV1/VC but TLC is not sufficiently reduced to diagnose restriction 1
• RV at 73% predicted and RV/TLC of 35% (80% predicted) are both normal, excluding air trapping or hyperinflation 1

Critical Interpretation Point

• The slightly reduced TLC (83%) with completely normal spirometry does not indicate pathology 1
• When TLC values lie near the lower limit of normal without corresponding spirometric abnormalities, this represents normal physiologic variation rather than disease 1

Diffusion Capacity

• DLCO is 97% predicted (Z-score -0.18), which is normal 1
• DLCO/VA is 106% predicted (Z-score 0.36), confirming normal alveolar-capillary membrane function 1
• Normal diffusion capacity excludes emphysema, interstitial lung disease, and pulmonary vascular disease 1

Flow Measurements

• FEF25-75% at 173% predicted is supranormal, further excluding small airway obstruction 1
• PEFR at 113% predicted is normal 1
• These elevated mid-expiratory flows definitively rule out the "small airways obstruction syndrome" pattern described in some patients with normal FEV1/FVC ratios 3, 4

Clinical Management Implications

No pulmonary interventions are indicated based on these results:

• No bronchodilator therapy is needed as there is no airflow obstruction or reversible component 1
• No further pulmonary function testing is required unless clinical symptoms develop 1
• These results provide normal baseline values for future comparison 1

Common Pitfalls to Avoid

• Do not misinterpret the slightly low TLC (83%) as restrictive disease when spirometry is completely normal 1
• Do not use the single-breath VA measurement (90% predicted) to diagnose restriction, as single-breath techniques systematically underestimate TLC and should never be used for this purpose 1
• Avoid applying a fixed FEV1/FVC ratio of 0.70 for obstruction diagnosis, as this leads to overdiagnosis particularly at extremes of age 1, 2
• Do not diagnose "small airways disease" based on isolated flow measurements when FEV1/FVC ratio and FEF25-75% are both normal to supranormal 1, 3, 4