Intra-session and inter-session variability of single-breath measurements of the diffusing capacities of the lung for nitric oxide (DLNO) and carbon monoxide (DLCO) (5 s breath hold) at rest

Test-to-test measurement error (within the same testing session)Repeatability# (within the same testing session)Reproducibility
(week-to-week or month-to-month change) More stringent
Smallest measurable change+ (week-to-week or month-to-month change) Less stringent
 mL·min−1·mmHg−16.2 (4)17 (10)20 (13)10 (7)
 mmol·min−1·kPa−12.1 (4)5.8 (10)6.5 (13)3.3 (7)
 mL·min−1·mmHg−11.2 (4)3.2 (10)4.9 (16)2.5 (8)
 mmol·min−1·kPa−10.4 (4)1.1 (10)1.6 (16)0.8 (8)
DLNO/DLCO ratio0.12 (2)0.36 (7)0.23 (5)0.13 (3)
 mL·min−1·mmHg−112 (7)34 (19)47 (28)24 (28)
 mmol·min−1·kPa−14.1 (7)11.2 (19)15.8 (28)8 (14)
VC mL4 (5)10 (13)16 (24)8 (12)
  • Numbers are presented as the value with the percentages in parentheses. Within-session data [49] and reproducibility data (between sessions) [88] were obtained from healthy subjects. The diffusing capacity of the membrane for carbon monoxide (DMCO), nitric oxide (DMNO) and total volume of blood in the lung capillaries exposed to alveolar air (VC) values are recalculations from the original dataset using the formulas and constants in table 4 as well as the supplementary appendices. The DLCO repeatability and reproducibility in subjects with pulmonary pathophysiology (mean DLCO 11–18 mL·min−1·mmHg−1) are 2.7 and 4 mL·min−1·mmHg−1, respectively [113, 114]. The repeatability was calculated as follows: the mean within-subject standard deviation (which is the average standard deviation between several diffusing capacity tests performed in one session) multiplied by 2.77. The reproducibility is performed the same way, except the mean week-to-week standard deviation is used (which is the average standard deviation between diffusing capacity measured over several weeks multiplied by 2.77). Refer to supplementary appendix G for in-depth statistical methodology of the calculation. #: the difference between two trials for DLNO, DLCO, DMCO and VC measured on the same subject in the same testing session is expected to be <17, <3.2 and <34 mL·min−1·mmHg−1 and <10 mL, respectively, for 95% of observations; : the difference in DLNO, DLCO, DMCO and VC measured on the same subject over two different weeks is expected to be less than 20, 4.9, and 47 mL·min−1·mmHg−1 and 16 mL, respectively, 95% of the time. Any diffusing capacity parameter that has a week-to-week or month-to-month change that is equal to or greater than the reproducibility has only a 5% chance that it is not a real change; +: half the reproducibility and thus less stringent than the reproducibility. Any week-to-week or month-to-month change that is equal to the smallest meaningful change has a 20% chance that it is not a real change. The reproducibility and smallest meaningful change are most correct when using the same equipment for the duration of the assessment.