Alterations of DLco diagnosis when using the first acceptable trial vs average of two acceptable trials

<bold>Introduction:</bold> Current ERS/ATS standards recommend that two acceptable DLco tests be averaged and this result compared to a lower limit of normal (LLN) for diagnosis. It may be possible to perform a single DLco test, improving efficiency. <bold>Objective:</bold> Our aim is to determine if using only the first acceptable DLco test changed the diagnosis when compared with using the average of the first two acceptable DLco tests. <bold>Methods:</bold> The COPDGene study measured DLco with a ndd EasyOne Pro instrument (Zurich, Switzerland) for phase II and III of the trial. One thousand subjects' DLco tests were randomly selected. Outliers were excluded. Demographics, LLN, first and second acceptable DLco tests were obtained. Subjects were categorized by two methods: 1) comparing the first DLco to the LLN (FirstDLco), 2) comparing the average of the first and second DLco tests to the LLN (AvgDLco). The SD of the absolute values of AvgDLco was calculated (SD_DLco). Changes in the diagnostic category betweeen FirstDLco and AvgDLco were determined. A subgroup (Close to LLN) was analyzed for changes in diagnosis when the FirstDLco was within 1.5 SD_DLco of the LLN (1.1 mL/min/mmHg). This group was thought to have a higher probability of a change in DLco categorization. <bold>Results:</bold> There were 974 subjects included. The SD_DLco was 0.73 mL/min/mmHg. Changes in diagnostic category between FirstDLco and AvgDLco are shown in Table. The percentage change in categorization for the subgroup Close to LLN (n=27) from FirstDLco to AvgDLco was 21.1% <bold>Conclusion:</bold> Our findings indicate that a single DLco test is sufficient for most patients. <table-wrap><object-id>erj;64/suppl_68/PA2592/TB1</object-id><object-id>T1</object-id><object-id>TB1</object-id><table><colgroup><col></col><col></col><col></col><col></col></colgroup><tbody><tr><td></td><td>FirstDLco above LLN</td><td>AvgDLco above LLN</td><td>Change in diagnosis</td></tr><tr><td>n</td><td>584/974</td><td>579/974</td><td>33/974</td></tr><tr><td>%</td><td>60.0%</td><td>59.5%</td><td>3.4%</td></tr></tbody></table></table-wrap>