How can a spirometry trial be considered usable but not acceptable according to American Thoracic Society (ATS) or European Respiratory Society (ERS) standards?

Understanding Usable vs. Acceptable Spirometry Trials

According to the American Thoracic Society (ATS) and European Respiratory Society (ERS) standards, a spirometry trial can be usable but not acceptable when it meets only the basic requirements for measurement but fails to meet all quality criteria for a fully acceptable test.

Criteria for Usable vs. Acceptable Spirometry Trials

Usable Curve Requirements (Minimum)

A spirometry curve is considered usable if it meets only these two basic conditions 1:

1. Has a satisfactory start of expiration (without excessive hesitation or false start with extrapolated volume <5% of FVC or 0.150 L, whichever is greater)
2. Is free from coughing during the first second of exhalation that would affect the FEV1 measurement

Acceptable Curve Requirements (Complete)

For a curve to be fully acceptable, it must meet all seven of these conditions 1:

1. Satisfactory start of expiration (as above)
2. No coughing during the first second or any cough affecting measurement
3. No early termination of expiration
4. No Valsalva maneuver or hesitation causing cessation of airflow
5. No leak at the mouth
6. No obstruction of the mouthpiece
7. No evidence of an extra breath during the maneuver

Clinical Implications

Why This Distinction Matters

• Data Retention: Even when a spirometry trial is not fully acceptable, it may still provide valuable clinical information 1. The ATS/ERS guidelines specifically state that "failure to meet these goals should not necessarily prevent reporting of results, since, for some subjects, this is their best performance."

• Special Populations: In patients with neuromuscular disorders, respiratory weakness, or other conditions that limit their ability to perform perfect spirometry, usable but not acceptable curves may represent their best possible effort 2, 3.

Common Reasons for Usable but Not Acceptable Trials

1. Early termination - Patient stops exhaling before reaching a plateau
2. Valsalva maneuver - Glottis closure during exhalation
3. Leaks - Air escaping around the mouthpiece
4. Obstructed mouthpiece - Due to tongue, teeth, or improper positioning

Practical Application

Test Selection Process

1. Collect at least three maneuvers
2. Identify which are usable (meeting minimum criteria)
3. Among those, identify which are fully acceptable (meeting all criteria)
4. Select the largest FVC and FEV1 values from acceptable curves
5. If no acceptable curves are available, usable curves may still provide clinically relevant information 1

Quality Control Considerations

• Documentation: When reporting spirometry results from usable but not acceptable trials, this limitation should be clearly documented 1
• Interpretation: The interpreter should consider the limitations when evaluating the clinical significance of the results
• Repeatability: Poor repeatability should not be the sole reason to reject results 1

Special Circumstances

Pediatric Patients

Young children may have difficulty meeting all acceptability criteria, particularly the end-of-test requirements, but their results may still be clinically useful 1, 2.

Patients with Neuromuscular Disease

Studies have shown that patients with conditions like spinal cord injury or Duchenne muscular dystrophy often cannot meet all ATS/ERS acceptability criteria but can still produce reproducible and clinically valuable spirometry data 2, 3.

By understanding the distinction between usable and acceptable spirometry trials, clinicians can maximize the clinical utility of pulmonary function testing while maintaining appropriate quality standards.