Introduction: The purpose of this analysis was to determine if abnormal diffusing capacity of the lung for carbon monoxide (DLco) identified a group of subjects with significantly different characteristics than those with normal lung function or airflow obstruction alone.
Methods: Participants were a random sample of adults aged 45-70 years. They completed a detailed respiratory questionnaire, spirometry, methacholine challenge and measurement of single breath DLco. Subjects were categorized into one of three groups: airflow obstruction only, reduced DLco only, or both airflow obstruction and reduced DLco.
Results: Individuals with airflow obstruction and reduced DLco in combination reported more symptoms than those with either condition alone. In subjects with a combination of both airflow obstruction and reduced DLco, a significantly higher proportion reported use of medication and laboratory tests. Current smoking was significantly associated with a reduced DLco alone and in combination with airflow obstruction, however, the association was stronger in those with DLco and airflow obstruction. Bronchial hyperreactivity (BHR) was found to be a risk factor while atopy was associated with a reduced risk of DLco and airflow obstruction.
Conclusions: Reduced DLco plus airflow obstruction together identifies a group of individuals with significantly more symptoms and worse lung function. Current cigarette smoking, early life serious respiratory infection and BHR were strongly associated with reduced DLco in combination with airflow obstruction.