Normal diffusing capacity in patients with piz α1-antitrypsin deficiency, severe airflow obstruction, and significant radiographic emphysema

α 1 -Antitrypsin deficiency is usually suspectedclinically in young adults with irreversible airflow obstruction thatis out of proportion to their smoking history. Many patients withα 1 -antitrypsin deficiency receive an initial diagnosis ofasthma or chronic bronchitis. Measurement of the diffusing capacity ofthe lung for carbon monoxide (Dlco) has been recommended asa way to help distinguish emphysema from asthma and chronic bronchitis. In this article, we describe four patients with severeα 1 -antitrypsin deficiency, each of whom had a repeatedlynormal Dlco despite having a significant component of fixedairway obstruction and prominent panacinar emphysema on high-resolutionCT scan (HRCT). Each patient also demonstrated significantbronchodilator responsiveness, and two patients received an initialdiagnosis of asthma. Potential explanations for these findings are discussed. We report these findings to illustrate the limitations of, Dlco in this setting. α 1 -Antitrypsindeficiency should be considered in patients with fixed airwayobstruction that is out of proportion to their age and smoking history, regardless of their diffusing capacity and response tobronchodilators.