Sensitivity of different spirometric tests for detecting airway obstruction in childhood asthma

Abstract

Objective: The objective of this study was to compare different measures of airflow obstruction by spirometry in childhood asthma. The objectives were; (a) to compare sensitivity of large airway tests (FEV₁ and PEFR) with tests at low lung volumes (small airways) (FEF_25–75, FEF₅₀ and FEF₇₅); (b) compare within each group which individual tests are more sensitive. Methods: This was a retrospective analysis of 2307 spirometry tests performed during outpatient visits on 821 doctor-diagnosed asthma patients aged 6–18. Tests were deemed acceptable if they were acceptable and repeatable by American Thoracic Society (ATS) criteria. Results: In mild obstruction, FEV₁ detected 6.8% abnormal tests while FEF₇₅ detected 33% (p < 0.0001). In more severe obstruction, the difference was more obvious (FEV₁ 14.8%; FEF₇₅ 71%). Tests at low lung volumes (small airway tests) were also more sensitive than PEFR. Within groups, FEV₁ was more sensitive than PEFR in the large airway tests and FEF₇₅ was more sensitive than FEF_25–75 and FEF₅₀ among the tests at low lung volumes (small airway tests). The FEV₁/FVC ratio correlated more closely with tests at low lung volumes (small airway tests), than with large airway tests. Conclusions: (1) Tests at low lung volumes (small airway tests) are more sensitive than large airway tests; (2) Within groups, the FEV₁ is better than PEFR and FEF₇₅ is better than FEF_25–75 or FEF₅₀.

• Asthma in children
• pulmonary function testing
• sensitivity of tests for obstruction
• specificity of tests for obstruction
• tests at low lung volumes (small airway obstruction)

Acknowledgements

The authors wish to thank Ms. Erin Jackson for typing the manuscript and Jennifer Andert BHS, RRT-NPS, and Mark Shiner BSOE, RRT, for helping with the data collection. Mr. Shiner also helped with normal spirometric test equations. Ms. Cynthia Haydon, BA, Senior Grant Writer, School of Medicine helped to edit the manuscript.

Declaration of interest

The authors have no financial, consulting or personal relationships with other people or organizations that could influence (bias) the authors’ work. Financial support was used from local funds from previous projects.