Validation of the lower limit of normal diffusing capacity for detecting emphysema.

Area of Science:

• Pulmonary Medicine
• Diagnostic Imaging
• Respiratory Physiology

Background:

• Diffusing capacity for carbon monoxide (D(Lco)) is a key indicator for emphysema.
• The current standard for the lower limit of normal (LLN) is the 5th percentile, lacking clinical validation.

Purpose of the Study:

• To validate the existing LLN for D(Lco) in emphysema detection.
• To identify the optimal LLN cutoff value for diagnosing emphysema.

Main Methods:

• Included 197 COPD patients and 103 healthy controls.
• Emphysema defined by volumetric CT criteria (>-950 HU >15% lung volume).
• Analyzed D(Lco) percentiles using ROC curve analysis.

Main Results:

• The 5th percentile LLN showed 68.3% sensitivity and 98.1% specificity.
• The 9th percentile demonstrated superior performance as an LLN cutoff for emphysema detection.

Conclusions:

• The traditional 5th percentile LLN for D(Lco) may be insufficient for accurate emphysema diagnosis.
• The 9th percentile represents a more effective threshold for identifying emphysema in COPD patients.