Applicability of the single-breath carbon monoxide diffusing capacity in aNorwegian community study

The test of single-breath diffusing capacity for carbon monoxide (DLCO) has been widely used in population surveys. However, little is known about the effect of meeting or failing to meet the criteria for acceptability of thi s test. The American Thoracic Society (ATS) recommends a breathholding time of 9 to 11 s, two measurements within +/- 10% or 3 mi CO(STPD)/min/mm Hg o f the average DLCO and an inspiratory vital capacity (IVC) of at least 90% of the largest previously measured forced vital capacity (FVC) as criteria for this test. The objective of the present study was to examine the extent to which these criteria were met in a community study. To do this, a rando m sample of 3,740 persons, aged 15 to 70 yr, of the general population of t he city of Bergen and 11 surrounding municipalities on the southwest coast of Norway were enrolled in a two-phase cross-sectional study. In the second phase, a stratified sample (n = 1,512) of the respondents to the postal qu estionnaire used for recruitment for the study (n = 3,370) were invited to a clinical and respiratory physiologic examination that included the DLCO t est. The attendance rate was 84% (1,275 of 1,512). In the examination, all subjects were able to maintain a breathholding time of 9 to 11 s, and 98% h ad two DLCO values within +/- 10% or 3 mi CO(STPD)/min/mm Hg of the average DLCO The criterion of an IVC of at least 90% of FVC in the two tests was m et by 68% of the subjects. Younger age was an independent predictor of fail ure to meet the required criteria. Thus, only two-thirds of the participant s fulfilled all of the ATS criteria for the DLCO test, the main reason for failure being an IVC of less than 90% FVC. This should not necessarily lead to the exclusion from further analysis of those failing to meet this crite rion.