Lactate dehydrogenase, creatine kinase, and their isoenzymes in pleural effusions

Lactate dehydrogenase (LD; EC 1.1.1.27) and creatine kinase (CK; EC 2.7.3.2) are widely distributed cytoplasmic enzymes. LD has five and CK has three isoenzymes distributed in different proportions in various tissues. The amounts of LD and CK and the distribution of isoenzymes in different body fluids are not thoroughly characterized. We have measured the total LD and CK concentrations and their isoenzyme distribution in pleural aspirates and in serum from 22 patients with benign conditions and from 14 patients with malignant effusions. In malignant pleural fluid, the mean total LD was 662 U/L; in benign conditions, it was nearly 5840 U/L with large variations (91-43 400 U/L) according to clinical diagnosis, the highest values being reached in inflammatory lesions. The mean total CK concentration in pleural fluid was close to the serum value in both groups of patients, as was the pleural CK isoenzyme distribution. The LD isoenzyme distribution in pleural effusions differed from that in serum in both groups, with LD-4 and -5 being the main isoenzymes in their pleural fluid specimens (greater than 42% of total LD). The total LD concentration correlated somewhat (r = 0.57) with the total pleural protein content. In conclusion, the pleural LD isoenzyme distribution, both in benign and malignant conditions, differs from that in serum, having shifted towards more anaerobic and embryonic isoenzymes (LD-4 and -5). Moreover, the greater the concentration of pleural total LD, the greater the proportion of LD-4 and -5. These data suggest that visceral or parietal pleural cells are rich in LD isoenzymes 4 and 5.