Veno-arterial difference in alpha 1 -antitrypsin levels.

alpha(1)-Antitrypsin levels, determined by radial immunodiffusion, were found to be higher in the venous than in the arterial blood of patients with pulmonary infections and in patients with obstructive airflow diseases. Large differences occurred in patients with both abnormalities. No difference was found in patients with other kinds of lung disease or in patients without lung disease. The veno-arterial difference probably occurs as blood passes through the lungs and probably results from alteration of the immunological properties of the alpha(1)-antitrypsin, perhaps by attachment to proteases, rather than absorption into the lung tissue. Further studies are needed to define the diseases in which this antienzyme plays an active part and to determine the mechanisms causing the difference.