What constitutes an acceptable spirometry trial?

Acceptable Spirometry Trial Criteria

An acceptable spirometry trial requires a satisfactory start of test, a satisfactory end of test with a plateau in the volume-time curve, and must meet seven specific conditions including proper technique, no coughing in the first second, no early termination, no glottis closure, no leaks, no mouthpiece obstruction, and no extra breaths during the maneuver. 1

Within-Maneuver Acceptability Criteria

For a spirometry trial to be considered acceptable, the following criteria must be met:

Technical Requirements:

1. Start of test: No excessive hesitation or false starts with extrapolated volume <5% of FVC or <0.150 L, whichever is greater 1
2. Free from artifacts:
   • No coughing during the first second (affects FEV1)
   • No glottis closure (Valsalva maneuver) affecting airflow
   • No hesitation causing cessation of airflow
   • No leaks at the mouth
   • No obstruction of the mouthpiece (by tongue, teeth, or biting)
   • No extra breaths during the maneuver 1
3. End of test: Satisfactory exhalation with either:
   • Duration >6 seconds (>3 seconds for children)
   • A plateau in the volume-time curve
   • Subject cannot or should not continue to exhale 1, 2

Important Distinction:

• A usable curve must only meet conditions 1 and 2 (good start and no cough in first second)
• An acceptable curve must meet all seven conditions listed above 1

Between-Maneuver Evaluation

For a complete spirometry test to be considered adequate:

1. Minimum requirements: At least three acceptable FVC maneuvers 1, 2
2. Repeatability criteria:
   • 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, these values should be within 0.100 L 1
3. Additional attempts: If repeatability criteria are not met after three maneuvers, additional trials should be performed (up to 8 maximum) 1, 2

Common Pitfalls and Caveats

• Poor technique: Large variability between tests often results from incomplete inhalations 1
• Test interpretation: Results from maneuvers with poor repeatability should not be automatically rejected but should be considered during interpretation 1
• Patient factors: Some patients may require brief rest periods between maneuvers 1
• Documentation: Volume-time or flow-volume curves from at least the best three FVC maneuvers must be retained 1
• Special populations: Patients with neuromuscular disease may require assistance to maintain an adequate seal at the mouth 1, 3
• Reporting: The reporting format should include qualifiers indicating the acceptability of each maneuver 1

Clinical Application

When evaluating spirometry results:

1. First determine if the test is valid using the criteria above
2. Only then proceed to interpret the results for diagnostic purposes 4

Even if a patient cannot meet all acceptability criteria, their best performance should still be recorded and considered, as it may contain useful clinical information 1.