Pleural effusion: a clinical review.

Pleural effusion is a problem commonly encountered by chest physicians, accounting for approximately 4% of all attendances to the chest clinic. In spite of extensive investigations, a significant proportion (approximately 20%) of effusions defy a diagnostic label. This article discusses the role of established, and some of the newer, techniques which are now available for investigating pleural disease in a clinical setting. The initial approach towards a diagnosis usually begins by distinguishing between transudates and exudates, based on protein and lactate dehydrogenase (LDH) concentrations in fluid (usually in relation to their concentration in serum). The exact role of amylase and LDH (and their isoenzymes) may provide additional information towards a differential diagnosis of various exudative pleural effusions. With newer cytochemical staining techniques on pleural fluid, the diagnostic yield of malignant pleural effusions may be increased by up to 80%. Ultrasound (US) and computed tomographic (CT) scan of the chest have further enhanced the diagnostic yield of undiagnosed pleural effusions, especially in relation to the US or CT guided needle biopsy. The re-emergence of thoracoscopy as the latest diagnostic and therapeutic (e.g. pleurodesis) tool for undiagnosed or recurrent pleural effusions, may help in narrowing the diagnostic dilemma faced by clinicians.