Abstract
Background: Some lung function laboratories perform 3 instead of 2 reproducible tests for the single-breath determination of the carbon monoxide diffusing capacity (DLCO) with the underlying assumption that the average of 3 values is more reliable than the average of 2. Recent ATS/ERS guidelines (Eur Respir J 2005) state that the actual number of tests that will provide the best estimate of DLCO is not yet determined.
Aim: To compare the within and between session variability of the DLCO estimate using 2 versus 3 values.
Methods: A DLCO measurement consisted of 3 acceptable tests that met the repeatability requirement according to the ATS/ERS guidelines. DLCO measurements were preferably performed twice a week on fixed, consecutive days just before lunchtime. A total of 10 DLCO measurements were collected in 12 nonsmoking, healthy adults (4M: 8F) during a 6 weeks period of time.
Results: The within and between session coefficients of variability (CoV) are listed in the table.
The determination of DLCO using 3 tests did not significantly reduce the within or between CoV compared to the use of only 2 tests. Although adding the third test to estimate DLCO significantly reduced the value of DLCO (p< 0.001), this reduction was not clinically relevant (∼1% reduction in the value of DLCO). For the average healthy subject the DLCO varied as much as ±7% (2 tailed 95% confidence interval) during a 6 weeks period of time.
Conclusion: A DLCO determination based on 3 instead of 2 tests does not result in a more stable estimate of DLCO.
- © 2011 ERS