What are the diagnostic criteria for lung disease on spirometry, including Forced Expiratory Volume in one second (FEV1) and Forced Vital Capacity (FVC)?

Diagnostic Criteria for Lung Disease on Spirometry

The diagnostic criteria for lung disease on spirometry include a post-bronchodilator FEV1/FVC ratio <0.7 to confirm obstructive airflow limitation, with severity classification based on FEV1 percentage of predicted value. 1, 2

Spirometry Quality and Acceptability Criteria

• Individual spirograms are considered acceptable when they are free from artifacts (cough, glottis closure, early termination), have good starts (extrapolated volume <5% of FVC or 0.15L), and show satisfactory exhalation (duration >6s or plateau in volume-time curve) 1
• Between-maneuver criteria require that the two largest values of FVC must be within 0.150L of each other, and the two largest values of FEV1 must be within 0.150L of each other 1
• A minimum of three acceptable spirograms should be obtained, with a practical upper limit of eight consecutive maneuvers 1
• The largest FEV1 and FVC should be recorded from all usable curves, even if they don't come from the same curve 1

Obstructive Lung Disease Criteria

• Airflow obstruction is defined by a post-bronchodilator FEV1/FVC ratio <0.7 1, 2

• Severity classification according to GOLD criteria 3, 2:

  • GOLD 1 (Mild): FEV1 ≥80% predicted
  • GOLD 2 (Moderate): FEV1 50-79% predicted
  • GOLD 3 (Severe): FEV1 30-49% predicted
  • GOLD 4 (Very Severe): FEV1 <30% predicted

• Pre-bronchodilator spirometry is recommended as an initial test to investigate airflow obstruction, but post-bronchodilator measurements are required to confirm the diagnosis of COPD 1, 2

• If the post-bronchodilator FEV1/FVC ratio is between 0.60 and 0.80, repeat spirometry on a separate occasion is recommended to confirm the presence or absence of airflow obstruction 1

Bronchodilator Response Patterns

• Volume responders: Patients with significant gas trapping who show greater improvement in FVC relative to FEV1 after bronchodilator administration 1

  • May have pre-BD FEV1/FVC ≥0.7 but post-BD FEV1/FVC <0.7 2
  • More common in patients with lower baseline FEV1 (e.g., <80% predicted) 1
  • Characterized by lower FEV1 and FVC, and higher residual volume 1

• Flow responders: Patients with greater FEV1 improvement relative to FVC 1

  • May increase FEV1/FVC from <0.7 pre-BD to ≥0.7 post-BD 1, 2
  • Require monitoring as they have increased likelihood of developing post-BD obstruction during follow-up 2

Special Considerations

• Using FEV1/SVC (slow vital capacity) instead of FEV1/FVC may increase sensitivity for detecting early obstructive disease 4
• The FEV1/SVC ratio may be more sensitive but less specific and adds complexity to lung function testing 1
• If there is strong clinical suspicion of COPD and the FEV1/FVC ratio is normal, further investigations could include assessment of the FEV1/SVC ratio 1
• Bronchodilator responsiveness testing has poor discriminative properties for differentiating COPD from asthma 2

Common Pitfalls and Caveats

• Using pre-BD values alone would lead to a significant increase in the number of patients diagnosed with COPD, putting additional pressure on health services 1, 2
• FVC may underestimate vital capacity in the presence of increased collapsibility of small airways, potentially causing the FEV1/FVC ratio to underestimate or fail to detect airflow obstruction 1
• Even spirometry results with lower quality grades (grade E or U) can be used for diagnostic purposes when carefully considered alongside clinical information 1
• Variability in FEV1/FVC results can arise due to variable expiratory times influencing the FVC values obtained 1

Monitoring Recommendations

• Follow-up should be scheduled in 4-6 weeks to assess response to therapy, inhaler technique, symptom control, and need for treatment adjustment 3, 2
• Annual spirometry is recommended to monitor disease progression 3, 2
• If the initial post-BD FEV1/FVC ratio is <0.60, it is very unlikely to rise spontaneously above 0.7 1