Intersession variability in single-breath diffusing capacity in diabetics without overt lung disease.

Area of Science:

• Pulmonary Function Testing
• Respiratory Physiology

Background:

• American Thoracic Society guidelines suggest a 10% intersession change in diffusing capacity of the lung (DLCO) is clinically significant.
• Limited data exist on DLCO short-term variability in untrained individuals and the impact of rigorous quality control.

Purpose of the Study:

• To characterize DLCO intersession variability in untrained individuals without lung disease.
• To assess the effect of different quality control methods on DLCO variability.

Main Methods:

• Pooled data from 14 preregistration trials of inhaled insulin.
• Compared DLCO measurements from 699 participants using a highly standardized technique versus 948 participants using routine clinical testing.

Main Results:

• Mean intersession DLCO change was 5.64% with standardization vs. 9.52% with routine testing (P < 0.0001).
• Variability increased with baseline DLCO, but percentage change remained stable.
• 15.5-35.5% of participants showed >=10% intersession change; a 20% threshold reduced this to 1-10%.

Conclusions:

• DLCO measurement variability depends on testing methodology and baseline DLCO.
• A more liberal threshold for defining significant intersession DLCO change could reduce misclassification of normal variation.