What are the American Thoracic Society (ATS) guidelines for assessing reversibility on spirometry?

American Thoracic Society Guidelines for Assessing Reversibility on Spirometry

According to the American Thoracic Society (ATS) guidelines, a positive bronchodilator response is defined as an increase in FEV1 or FVC of at least 12% AND 200 mL from baseline values after bronchodilator administration. 1

Bronchodilator Administration Protocol

Standardized Dosing

• For metered dose inhalers (MDIs):
  • Standard dose: 400 μg of salbutamol (albuterol) 1
  • Delivery method: Preferably with a valve-holding chamber (spacer) to improve lung deposition
  • Expected lung deposition: 10-20% of each 100 μg "puff" (approximately 15 μg per activation)

Testing Procedure

1. Perform baseline spirometry following ATS standards for acceptability and repeatability
2. Administer bronchodilator according to standardized protocol
3. Wait 10-15 minutes after bronchodilator administration
4. Perform post-bronchodilator spirometry

Spirometry Quality Standards

Within-Maneuver Acceptability Criteria

• Free from artifacts:
  • No cough during first second of exhalation
  • No glottis closure affecting measurement
  • No early termination or cut-off
  • Maximal effort throughout
  • No leak
  • No obstructed mouthpiece
  • No extra breaths during maneuver
• Good start of test:
  • Extrapolated volume < 5% of FVC or 0.15 L (whichever is greater)
• Satisfactory exhalation:
  • Duration > 6 seconds (3 seconds for children) or plateau in volume-time curve 1

Between-Maneuver Repeatability Criteria

• Minimum of three acceptable FVC maneuvers
• The two largest FVC values must be within 0.150 L of each other
• The two largest FEV1 values must be within 0.150 L of each other
• For patients with FVC ≤ 1.0 L, both criteria are reduced to 0.100 L 1

Determining Reversibility

Definition of Positive Bronchodilator Response

• An increase in FEV1 OR FVC of:
  • ≥ 12% from baseline AND
  • ≥ 200 mL absolute change 1, 2

Assessment Protocol

1. Calculate percent change: [(Post-bronchodilator value - Pre-bronchodilator value) / Pre-bronchodilator value] × 100
2. Calculate absolute change: Post-bronchodilator value - Pre-bronchodilator value
3. Both criteria (percentage and absolute change) must be met for a positive response

Clinical Implications

• A positive bronchodilator response supports but does not definitively diagnose asthma
• Lack of bronchodilator response does not exclude asthma
• For COPD severity assessment, post-bronchodilator FEV1 values should be used 3
• Post-bronchodilator values are essential for proper COPD classification and to avoid overdiagnosis 4

Important Considerations

Post-Bronchodilator Testing Importance

• Using post-bronchodilator values is critical for COPD assessment
• Studies show that 20% of patients may change COPD severity classification when post-bronchodilator values are used instead of pre-bronchodilator values 3
• Approximately 7.3% of subjects may change from obstructed to non-obstructed status after bronchodilator administration 5

Common Pitfalls to Avoid

• Using pre-bronchodilator values for COPD severity classification can lead to overestimation of disease severity
• Confusing "bronchodilator responsiveness" with "reversibility of obstruction" - these terms are not interchangeable 5
• Failing to meet quality standards for spirometry, which can invalidate reversibility assessment
• Not allowing adequate time between bronchodilator administration and post-bronchodilator testing

Alternative Assessment Methods

For patients who cannot perform acceptable spirometry maneuvers:

• Body plethysmography (measuring airway resistance)
• Transcutaneous oxygen tension measurements (particularly useful in children)
• Forced oscillation techniques (effort-independent) 1, 6

By following these standardized guidelines for bronchodilator reversibility testing, clinicians can ensure accurate assessment of airflow obstruction and appropriate clinical decision-making for patients with respiratory symptoms.