Pleural effusions: seeing transudate–exudate differentiation in a different light

Extract Pleural effusions are a common medical presentation, with an estimated incidence of 337 per 100 000 of the population [1]. The causes of pleural effusion are diverse and making an accurate diagnosis is therefore paramount. A typical first step in the evaluation of patients with pleural effusion is to differentiate the effusion as a transudate or exudate [2]. Transudates are a result of systemic factors leading to increased capillary hydrostatic pressure or reduced oncotic pressure, while exudates reflect an inflamed pleura with causes including malignancy, infection and autoimmune conditions.