Normal diffusing capacity in patients with PiZ alpha(1)-antitrypsin deficiency, severe airflow obstruction, and significant radiographic emphysema

alpha(1)-Antitrypsin deficiency is usually suspected clinically in young ad ults with irreversible airflow obstruction that is out of proportion to the ir smoking history, Many patients with alpha(1)-antitrypsin deficiency rece ive an initial diagnosis of asthma or chronic bronchitis. Measurement of th e diffusing capacity of the lung for carbon monoxide (DLCO) has been recomm ended as a way to help distinguish emphysema from asthma and chronic bronch itis. In this article, we describe four patients with severe alpha(1)-antit rypsin deficiency, each of whom had a repeatedly normal DLCO despite having a significant component of fixed airway obstruction and prominent panacina r emphysema on high-resolution CT scan (HRCT). Each patient also demonstrat ed significant bronchodilator responsiveness, and two patients received an initial diagnosis of asthma. Potential explanations for these findings are discussed. We report these findings to illustrate the limitations of DLCO i n this setting. alpha(1)-Antitrypsin deficiency should he considered in pat ients with fixed airway obstruction that is out of proportion to their age and smoking history, regardless of their diffusing capacity and response to bronchodilators.