Validation of the Lower Limit of Normal Diffusing Capacity for Detecting Emphysema

BACKGROUND:: Diffusing capacity for carbon monoxide (DLco) has been regarded as reliable for detecting emphysema. The lower 5th percentile of the reference population has been used as the lower limit of normal (LLN) for DLco, without clinical validation. OBJECTIVES:: We performed this study to validate the LLN for DLco and to determine the optimum cutoff LLN value for detecting emphysema. METHODS:: A total of 197 COPD patients and 103 healthy adult subjects were included. COPD patients with emphysema were defined as COPD patients in whom volumetric CT showed that the volume fraction of the lung at less than ?950 Hounsfield units at full inspiration was more than 15%. All other COPD patients were defined as COPD patients without emphysema. All measured DLco values were transformed to estimates of reference population percentiles. ROC curve analysis was used to validate and to determine the optimum cutoff percentile value as the LLN for DLco. RESULTS:: Of the 197 COPD patients, 126 were classified as having emphysema and 71 as without emphysema. On ROC curve analysis, the lower 5th percentile used as the LLN for DLco had a sensitivity of 68.3% and a specificity of 98.1% to differentiate COPD patients with emphysema from healthy subjects. The lower 9th percentile was the best LLN cutoff value for detecting COPD patients with emphysema. CONCLUSION:: The lower 5th percentile of the reference population may not be the best LLN cutoff value for DLco for detecting emphysema.Copyright ??? 2010 S. Karger AG, BaselThe authors thank the members of the Korean Obstructive Lung Disease (KOLD) cohort study group. This study was supported by a grant (A040153) from the Korean Health 21 R&D Project, Ministry of Health, Welfare and Family Affairs, Republic of Korea and by the Asan Institute for Life Science (04-306).J.B.S. has been an investigator in a government-sponsored study (2006-2008, Korea Science and Engineering Foundation). Y.-M.O. has been an investigator in university-sponsored studies (University of Ulsan College of Medicine) and an industry-sponsored study (AstraZeneca Korea), and has participated as a speaker in scientific meetings organized and financed by various pharmaceutical companies (GlaxoSmithKline, AstraZeneca Korea, MSD Korea, and Boehringer Ingelheim). S.-D.L. serves as a consultant to GlaxoSmithKline and has participated as a speaker in scientific meetings organized and financed by various pharmaceutical companies (GlaxoSmithKline, AstraZeneca Korea, and Boehringer Ingelheim)