Specific Gravity of Pleural Fluid Determined by Refractometer to Discriminate Exudates and Transudates

摘要

The first diagnostic step in pleural fluid analysis in patients with pleural effusion is differentiating transudates from exudates. This study was done with the objective of determining the sensitivity and specificity of pleural fluid specific gravity in differentiating transudate from exudate fluids. Hundred patients (71 males and 29 females) with pleural effusion, who were referred to the pulmonary ward of the university hospital, underwent diagnostic thoracentesis. According to Light's criteria exudates and transudates were distinguished. Then, pleural fluid specific gravities were determined by refractometer. All patients were followed, until final diagnoses were documented by invasive and/or non-invasive methods. We calculated sensitivity, specificity, positive and negative predictive values of different specific gravities to obtain the optimal cutoff value. Seventy percent patients were diagnosed as having exudative pleural effusion and 30% patients with transudative effusion. The mean (SD) specific gravity in patients with exudative and transudative pleural effusion were 1033.6 (7.05) and 1021.4 (4.45), respectively (p<0.05). Optimal sensitivity and specificity were achieved at a cutoff value of 1024. At this cutoff value sensitivity, specificity, positive predictive value and negative predictive value were 91.4, 66.7, 86.5 and 76.9%, respectively. Specific gravity of pleural fluid was found to be a simple and sensitive method for distinguishing between transudates and exudates.