Spirometry
Considerations:
- Reference ranges are derived from healthy population (GLI reference equations for spirometry) and indicate expected values.
- Utilizing the 5th and 95th percentiles, corresponding to -1.645 and +1.645 z-scores, helps identify individuals with notably low or high results.
- The LLN can be adjusted based on pre-test probability. For PFTs in low-risk scenarios, like general screenings, a more conservative LLN (e.g., 2.5% or -1.96 z-score, 1% or -2.326 z-score) reduces false positives.
- Documentation of the chosen LLN in PFT reports is essential.
Bronchodilator Responsiveness
ERS/ATS: > 10% change relative to the predicted value, respectively.
Considerations:
- The ATS/ERS guidelines suggest assessing bronchodilator responsiveness by calculating changes as a percentage of the predicted value, instead of basing them on pre-bronchodilator measurements.
- PEF and FEF25–75% measurements are highly variable and influenced by FVC changes, making direct comparison of pre- and post-bronchodilator values unreliable.
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.