Levels of angiotensin-converting enzyme in pleural effusion

The value of determining the angiotensin-converting enzyme (ACE) in serum has been clearly established, particularly in sarcoidosis, but is significance in pleural effusions is practically unknown. In the present study, ACE level was determined in the pleural fluid of 18 hospitalized patients along with the values for total protein, lactic acid dehydrogenase (LDH), complete and differential cell counts and cytology. The ACE level was higher in exudates than in transudates and paralleled closely the total protein level in the pleural fluid. There was no correlation between ACE and LDH levels and either WBC or RBC counts in the effusions. The ACE levels failed to discriminate between benign and malignant diseases or to correlate with any specific etiology for the effusion. There was a significant gradient between ACE levels that were higher in the serum than in the effusion of all nine patients in whom both were measured. The filtration coefficient (ratio of pleural fluid to serum concentration of a protein) of ACE was less than that of total protein and was compatible with ACE penetration in the pleural fluid by a process of diffusion.