Accuracy of serum/pleural fluid lactate dehydrogenase ratio measurement in patients with malignant pleural effusion

Background: Several human tumors release lactate dehydrogenase (LDH) that is involved in anaerobic glycolysis, and LDH serum level usually increases in cancer patients. Unfortunately, both sensitivity and specificity of serum LDH is low and thus not useful for early diagnosis of malignancy. The aim of this study was to evaluate the accuracy of serum LDH measurement and serum/pleural fluid LDH ratio (SPLR) in patients with benign and malignant pleural effusions. Methods: Serum and pleural LDH was measured in a population (cases) of 117 cancer patients (mean age: 68.2±10.1 years) with malignant pleural effusion. There were 48 non-small-cell lung cancer (NSCLC), 38 patients with lung metastases, and 31 patients with pleural mesothelioma. Controls were 36 age-matched patients (mean age: 69.1±13.5 years, p=0.67) with confirmed benign pleural effusion. A standard commercially available colorimetric LDH activity assay kit was used. Results: Serum/pleural fluid LDH ratio was lower in patients with lung metastases (0.63±0.14) with respect to those with NSCLC (0.90±0.71, p=0.042) and pleural mesotheliomas (1.08±0.66, p=0.0004). Overall, serum LDH and SPLR (cases vs. controls) were 260.8±243.6 vs. 371.6±607.4 IU/L (p=0.11) and 0.90±0.60 vs. 1.23±1.14 (p=0.024), respectively. For SPLR, a cut-off level of 0.5 showed 93.1% sensitivity and 97.22% specificity. The Table below reports the other results. Conclusions: The measurement of SPLR represents an accurate and low-cost laboratory method, especially useful when metastatic or non-small-cell lung cancer are suspected, and should be suggested in all patients with pleural effusions.