How is spirometry (spirometry) interpreted and what are the treatment options for abnormal results?

Spirometry Interpretation and Management of Abnormal Results

Spirometry interpretation should follow a standardized approach with abnormal results defined by values below the lower limit of normal (LLN) rather than fixed cutoffs, as this provides more accurate clinical assessment across different age groups.

Standardized Approach to Spirometry Interpretation

Step 1: Assess Technical Quality

• Evaluate test quality using grading system (A through F) 1
  • Tests with grades A, B, or C are usable
  • Tests with grade D are suspect
  • Tests with grade E may only show values "within normal range"
• Ensure at least 3 acceptable maneuvers were performed
• Verify reproducibility criteria were met

Step 2: Identify Ventilatory Pattern

1. Examine FEV1/FVC ratio:

   • Compare to LLN (not the fixed 0.70 cutoff)
   • Fixed cutoff of 0.70 leads to false positives in older adults 1
   • LLN should be calculated as the 5th percentile of reference population 1, 2
   • A practical approximation: subtract 0.10 from age-specific predicted FEV1/FVC 2

2. Examine FVC:

   • Compare to LLN (not the fixed 80% predicted)
   • Values below 5th percentile in adults or <80% predicted in children 5-18 years are abnormal 3

3. Determine pattern:

   • Obstructive: Reduced FEV1/FVC ratio below LLN
   • Restrictive: Normal/increased FEV1/FVC with reduced FVC below LLN
   • Mixed: Reduced FEV1/FVC and reduced FVC

Step 3: Assess Severity

• Based on FEV1 percent predicted:
  • Mild: FEV1 ≥70% predicted
  • Moderate: FEV1 60-69% predicted
  • Moderately severe: FEV1 50-59% predicted
  • Severe: FEV1 35-49% predicted
  • Very severe: FEV1 <35% predicted

Step 4: Evaluate Bronchodilator Response (if obstructive pattern)

• Positive response defined as:
  • Increase in FEV1 or FVC ≥12% AND ≥200 mL in adults 4
  • Increase >12% in children and adolescents 5-18 years 3

Management of Abnormal Results

For Obstructive Pattern

1. Assess reversibility with bronchodilator testing
2. If reversible (positive bronchodilator response):
   • Consider asthma diagnosis, especially with FeNO ≥25 ppb 1
   • Initiate appropriate controller therapy
3. If not reversible:
   • Consider COPD if risk factors present
   • Consider additional testing (lung volumes, DLCO)

For Restrictive Pattern

1. Confirm with lung volumes (TLC measurement)
2. Consider causes:
   • Interstitial lung disease
   • Chest wall disorders
   • Neuromuscular weakness
   • Pleural disease
   • Obesity
3. Additional testing as indicated (HRCT, DLCO)

For Normal Spirometry with Persistent Symptoms

1. Consider additional testing:
   • FeNO measurement (≥25 ppb suggests asthma) 1
   • Peak flow variability testing (≥12% suggests asthma) 1
   • Bronchoprovocation testing for suspected asthma 3

Special Considerations

Longitudinal Monitoring

• Evaluate decline in FEV1 over time:
  • Normal decline in nonsmokers: ~29 mL/year 1
  • Accelerated decline (>60-90 mL/year) associated with increased morbidity and mortality 1
• Methods to identify excessive decline:

  • 15% decline from baseline FEV1 (plus expected age-related loss) 1

  • Use of computer software to determine limit of longitudinal decline 1

Ethnic Considerations

• Use ethnically appropriate reference values:
  • NHANES III for White, African American, and Hispanic populations 1
  • Apply correction factor of 0.88 for Asian-Americans 1
  • Regional reference equations when available (e.g., Western Indian population has lower lung volumes) 5

Common Pitfalls to Avoid

1. Using fixed cutoffs instead of LLN:

   • Fixed FEV1/FVC ratio of 0.70 overdiagnoses obstruction in elderly 1
   • Fixed 80% predicted cutoff misclassifies individuals based on age and height 2

2. Interpreting MEF values in isolation:

   • Mid-expiratory flow values (MEF 25-75%) should always be interpreted alongside FEV1 and FEV1/VC 6
   • Abnormal MEF values with normal FEV1 and FEV1/VC have limited clinical significance 6

3. Failing to consider posture effects:

   • Document whether testing was performed sitting or standing
   • Use consistent posture for longitudinal testing 1

4. Overlooking technical factors:

   • Poor effort can significantly impact results
   • Chest binders in transgender individuals can affect measurements 1

By following this systematic approach to spirometry interpretation and management, clinicians can accurately identify abnormalities and initiate appropriate treatment or further evaluation to improve patient outcomes.