A novel diagnostic method for distinguishing parapneumonic effusion and empyema from other diseases by using the pleural lactate dehydrogenase to adenosine deaminase ratio and carcinoembryonic antigen levels.

Pleural effusions are a common medical problem not only for pulmonologists but also for general physicians, often needing thoracentesis for a definite diagnosis. However, thoracentesis cannot always reveal malignant cells or microbiological evidence. In this context, we prospectively enrolled a total of 289 patients with pleural effusions due to diverse etiologies: parapneumonic effusion (PPE) (63), empyema (22), tuberculous pleural effusion (TBPE) (54), malignant pleural effusion (MPE) (140), or chronic renal failure (CRF)/congestive heart failure (CHF) (10). The MPE group consisted of lung cancer (adenocarcinoma, n=90; squamous cell carcinoma, n=5; small cell carcinoma, n=4), malignant lymphoma (n=17), malignant mesothelioma (n=11), malignant melanoma (n=3), and metastasis from other organs (n=10). This study demonstrated that the pleural lactate dehydrogenase (LDH) to adenosine deaminase (ADA) ratios differed significantly between patients with CHF/CRF, MPE, TBPE, empyema, and PPE. We discovered a simple method to differentiate pleural diseases based on the pleural LDH to ADA ratio and carcinoembryonic antigen (CEA). A pleural LDH to ADA ratio greater than 15.5 and a pleural CEA level of less than 5ng/mL is indicative of PPE or empyema rather than TBPE, MPE, or transudative pleural effusion (CRF, CHF). This method has a sensitivity of 62.0%, a specificity of 91.0%, and an area under the receiver operating characteristic curve of 0.765 (95% confidence interval [CI]: 0678-0.852, P<.001), odds ratio of 16.6 (95% CI: 7.28-37.8, P<.001), a positive likelihood ratio (LR) of 6.8, and a negative LR of 0.02.