Standardization of the single-breath determination of carbon monoxide uptake in the lung. ATS/ERS Task Force on "Standardization of Lung Function Testing"

This section, mainly drafted by N. MacIntyre, R. Crapo, G. Viegi, D.C. Johnson and C.P.M. van der Grinten, stirred up some controversy first in the drafting of the document and again in the comments received from reviewers. The areas of concern were primarily related to adjustments of DL,CO for lung volume (i.e. the use of DL,CO/alveolar volume (VA)) and how to interpret unadjusted and adjusted values if the decision was to adjust for lung volume. All agreed that the DL,CO relationship to VA is complex, and that the simple DL,CO/VA value does not necessarily ''correct'' for a reduced DL,CO in the setting of a comparably reduced VA. There was also a significant discussion over how to deal with adjustments for haemoglobin and carboxyhaemoglobin concentrations. Upon recognition that adjustments for haemoglobin are under-utilised, we decided to adjust for these, but the adjustments need to be made to the predicted rather than the measured values. After the document was finalised, several committee members were informally polled to find out how they personally use DL,CO/VA. The responses mirrored the review process. There was wide variation, ranging from ''do not use it at all'' and ''do not print it on the report'' to saying something about it on every interpretation. This variation amongst committee members suggests that more research on the clinical utility of DL,CO/VA is required, to be possibly included in a future version. The decision to use the term DL,CO rather than the carbon monoxide transfer factor (TL,CO) was not controversial until the document went for outside review. Everyone on the Task Force understood that TL,CO is more correct from a terminology and scientific standpoint, but perhaps it was the long history of DL,CO and its common usage that gave it the edge. Exercise and positional changes in DL,CO were not addressed, although it was recognised that they may provide an assessment of capillary recruitment and might, therefore, be useful clinically, and this may be another addition for a future version.