Lung function testing: the dilemma of predicted values in relation to the individual variability

Area of Science:

• Pulmonary Medicine
• Diagnostic Testing
• Biostatistics

Background:

• Lung function parameters are typically assessed against population-derived normal ranges.
• The reliability of these population-based normal ranges for individual assessment is questioned due to variability.

Purpose of the Study:

• To critically review formulas used for lung function testing.
• To evaluate the extent of intra-individual variation in lung function measurements.
• To determine if population-based normal ranges are adequate for individual interpretation.

Main Methods:

• Conducted 30-72 repeated spirometric and body plethysmographic measurements over 2 months in 26 healthy subjects.
• Utilized established formulas for predicted lung function values (Quanjer et al., Ulmer et al., Ruehle and Matthys).
• Analyzed variations due to intra-individual changes over time and inter-individual differences, adjusting for medical center variations.

Main Results:

• Intra-individual standard deviation was approximately half of the inter-individual standard deviation.
• Population-derived normal ranges for lung function parameters were found to be excessively wide for individual assessment.
• The contribution of intra-individual variation to overall parameter variation was significant.

Conclusions:

• Population-based normal ranges are too broad for accurate individual lung function assessment.
• Interpretation of individual lung function measurements should prioritize an "individual normal range" established from prior measurements.
• Predicted values should serve as a secondary reference for interpreting lung function data.