Activity of angiotensin-converting enzyme in pleural fluid and serum in non-sarcoid, non-tuberculous pleural effusion.

The activity of angiotensin-converting enzyme (ACE) was measured in pleural fluid (PACE) and serum (SACE) from 25 patients with pleural effusion due to cancer or non-malignant diseases. In all patients SACE was within normal limits. One patient with a rheumatic pleuritis had a PACE/SACE ratio greater than 3.0, but among the remaining 24 patients PACE was 12.1 +/- 6.5 U/ml (mean +/- 1 SD), and SACE was 21.9 +/- 6.4 U/ml (P less than 0.005), with a PACE/SACE ratio of 0.58 +/- 0.31. SACE and PACE were positively correlated in patients with exudative pleuritis (P less than 0.01). In hydrothorax due to congestive heart failure a very low PACE/SACE ratio was found. Enzyme activity or ratio was correlated to protein content (P less than 0.02) but not to aetiology of pleural effusion, presence of malignant cells, leucocyte- pr erythrocyte content. In general, measureable CE activity can be detected in pleural fluid, but this finding seems at present to have no clinical significance in these conditions.