Diagnostic Significance of Lactic Dehydrogenase Isoenzymes in Pleural Effusions

Simultaneous pleural and serum lactic dehydrogenase (LDH) enzyme activity was determined in 150 consecutive patients with pleural effusions (120 benign and 30 malignant), and isoenzyme analysis was performed. The mean pleural fluid LDH activity was significantly higher in patients with empyema and non-specific pleurisy than in patients with tuberculosis, malignancy and congestive heart failure. Patients with malignancy showed higher mean pleural fluid LDH activity than those with congestive heart failure. According to isoenzyme analysis, the fraction of LDH3 was high in one third of the malignant pleural effusion, patients. Pleural fluids in patients with empyme and tuberculosis were characterized by a reduction in LDH4 and LDH5, while their LDH3 activity was significantly high as in the malignant group. No definitive relationship was found between the histologic pattern of the malignancy on the LDH isoenzyme pattern. According to these findings, we have concluded that neither the total LDH activity in serum and pleural fluids nor the LDH isoenzymes can help us differentiate between malignant pleural effusion and various types of exudative pleural effusions.