Intersession variability in single-breath diffusing capacity in diabetics without overt lung disease.
BACKGROUND
American Thoracic Society guidelines state that a 10% or greater intersession change in diffusing capacity of the lung (DL(CO)) should be considered clinically significant. However, little is known about the short-term intersession variability in DL(CO) in untrained subjects or how variability is affected by rigorous external quality control.


OBJECTIVE
To characterize the intersession variability of DL(CO) and the effect of different quality control methods in untrained individuals without significant lung disease.


METHODS
Data were pooled from the comparator arms of 14 preregistration trials of inhaled insulin that included nonsmoking diabetic patients without significant lung disease. A total of 699 participants performed repeated DL(CO) measurements using a highly standardized technique. A total of 948 participants performed repeated measurements using routine clinical testing.


RESULTS
The mean intersession absolute change in DL(CO) using the highly standardized method was 1.45 ml/minute/mm Hg (5.64%) compared with 2.49 ml/minute/mm Hg (9.52%) in the routine testing group (P < 0.0001 for both absolute and percent difference). The variability in absolute intersession change in DL(CO) increased with increasing baseline DL(CO) values, whereas the absolute percentage of intersession change was stable across baseline values. Depending on the method, 15.5 to 35.5% of participants had an intersession change of 10% or greater. A 20% or greater threshold would reduce this percentage of patients to 1 to 10%.


CONCLUSIONS
Intersession variability in DL(CO) measurement is dependent on the method of testing used and baseline DL(CO). Using a more liberal threshold to define meaningful intersession change may reduce the misclassification of normal variation as abnormal change.
Drummond
Michael B
MB
Division of Pulmonary and Critical Care Medicine, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21224, USA. mdrummo3@jhmi.edu
Schwartz
Pamela F
PF
Duggan
William T
WT
Teeter
John G
JG
Riese
Richard J
RJ
Ahrens
Richard C
RC
Crapo
Robert O
RO
England
Richard D
RD
Macintyre
Neil R
NR
Jensen
Robert L
RL
Wise
Robert A
RA
D000328:Adult; D000368:Aged; D003922:Diabetes Mellitus, Type 1; D003924:Diabetes Mellitus, Type 2; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011653:Pulmonary Diffusing Capacity; D012016:Reference Values; D015203:Reproducibility of Results; D012129:Respiratory Function Tests / Q000379:methods*