A Study of Serum to Pleural Fluid Albumin Gradient in Differentiation of Exudative and Transudative Pleural Effusion in Comparison to Light’s Criteria

Pleural effusion is the accumulation of fluid between the parietal and visceral pleura called the pleural cavity. It can occur by itself or can be the result of surrounding parenchymal diseases like infection, malignancy or inflammatory conditions. Pleural effusion is one of the major causes of pulmonary mortality and morbidity. Both the visceral and the parietal pleura play an important role in fluid homeostasis in the pleural space. Pleural effusions develop when there is excess hydrostatic pressure in the pulmonary capillaries, when fluid removal is impaired by compromised lymphatic drainage or when protein and cell rich fluid enters the pleural space through leaky capillary and pleural membranes. Pleural fluid is classified as a transudate or exudate based on modified Light’s criteria, proposed by Light et al., in 1972 which has been the standard differentiation method. It is considered an exudative effusion if at least one of the criteria is met:  Pleural fluid protein/serum protein ratio of more than 0.5  Pleural fluid lactate dehydrogenase (LDH)/serum LDH ratio of more than 0.6  Pleural fluid LDH is more than two-thirds of the upper limits of normal laboratory value for serum LDH. Commonly performed tests on the pleural fluid to determine etiology are a measurement of fluid pH, fluid protein, albumin and LDH, fluid glucose, fluid triglyceride, fluid cell count differential, fluid gram stain and culture and fluid cytology.