Spirometry
Considerations:
- Reference Values: GLI equations describe the distribution of values expected in a healthy population.
- Limits of Normal: The 5th and 95th percentiles (z-scores of ±1.645) serve as unbiased boundaries for unusually low or high results.
- Meaning of LLN: The LLN represents the bottom 5% of the healthy population. It is a statistical cut-off, not a definitive diagnostic threshold.
- Clinical Adjustment: For low-risk cases, adjusting the LLN based on pre-test probability (e.g. using the 1st percentile) can reduce false positives.
Bronchodilator Responsiveness
ERS/ATS (2022): > 10% change relative to the predicted value, respectively.
Considerations:
- Reversibility: Do not confuse BDR with reversibility (normalization of FEV1/FVC).
- Air Trapping: BDR in FVC may better reflect air trapping and hyperinflation than FEV1.
- Flow Rates: PEF and FEF25–75% are not comparable pre- and post-bronchodilator due to volume dependency.
- Legacy Methods: Avoid using absolute or % change from baseline (e.g. 200mL and 12%), as these are biased by baseline lung function.
Bronchoprovocation
ERS/ATS: PD20: provocative dose causing a > 20% change in the FEV1.
Lung Volumes
Diffusion
Severity Assessment
Considerations:
- Use Z-scores to assess lung function impairment severity. Z-scores provide a standardized measure across different populations.
- Differentiate between lung function impairment severity and overall disease severity. Lung function impairment severity is based on test results, while disease severity considers additional factors like quality of life, daily functioning, and imaging results.