Spirometry Repeatability Criteria
Acceptable repeatability is achieved when the difference between the two largest FVC values is ≤0.150 L AND the difference between the two largest FEV₁ values is ≤0.150 L, with a lower threshold of ≤0.100 L for both parameters when FVC is <1.0 L. 1
Minimum Testing Requirements
- At least three acceptable maneuvers must be performed to assess repeatability 1
- Continue testing until repeatability criteria are met, up to a maximum of eight maneuvers (though this is optional) 1
- If repeatability criteria are not met after three maneuvers, additional trials should be attempted 1
Specific Repeatability Thresholds
Standard Adult Criteria
- FVC repeatability: The two largest values must be within 0.150 L of each other 1
- FEV₁ repeatability: The two largest values must be within 0.150 L of each other 1
Low Volume Exception
- For patients with FVC ≤1.0 L, both thresholds are reduced to 0.100 L 1
Critical Implementation Points
Which Maneuvers to Include
- Only "acceptable" maneuvers (meeting all within-maneuver criteria) should be used for repeatability assessment 1
- Maneuvers with an unacceptable start-of-test or cough must be discarded before applying repeatability criteria 1
- Maneuvers with early termination or Valsalva maneuver may still be used for selecting the largest FVC and FEV₁ values 1
When to Stop Testing
The test session may be concluded when: 1
- Both repeatability criteria are met (FVC and FEV₁ within thresholds)
- OR a total of eight tests have been performed
- OR the patient cannot or should not continue
Common Pitfall: Patient Fatigue
- Large variability among tests is often due to incomplete inhalations rather than poor effort 1
- Some patients may require a brief rest period between maneuvers to improve repeatability 1
- After several forced expiratory maneuvers, fatigue can reduce performance, making additional maneuvers of little value 1
Safety Consideration
Terminate testing immediately if there is a progressive reduction in FEV₁ or FVC with a cumulative drop exceeding 20% of the start value, as this poses a patient safety concern 1
Important Clinical Caveat
Repeatability criteria should NOT be used to exclude results from reports or exclude subjects from studies 1. Poor repeatability should be documented and considered during interpretation, but results should still be reported as they may represent the patient's best performance 1. The repeatability criteria are minimum requirements to determine when additional maneuvers are needed, not rejection criteria 1.