Thoracentesis is a percutaneous procedure during which a needle is inserted into the pleural space and pleural fluid is removed either through the needle or a small bore catheter. "Diagnostic thoracentesis" refers to removal of a small volume of pleural fluid for analysis, while "therapeutic thoracentesis" refers to removal of a large volume of pleural fluid for relief of symptoms.
The indications, contraindications, technique, and complications of diagnostic thoracentesis will be reviewed here. Pleural fluid analysis, pleural manometry, and large volume thoracentesis are discussed separately. (See "Diagnostic evaluation of a pleural effusion in adults: Initial testing" and "Diagnostic evaluation of pleural effusion in adults: Additional tests for undetermined etiology" and "Measurement of pleural pressure" and "Large volume thoracentesis".)
Pleural effusions are usually detected by physical examination or by thoracic imaging studies. Imaging by ultrasonography, standard radiographs or chest CT is always necessary to confirm the presence of an effusion before proceeding to thoracentesis. Most patients who have a pleural effusion should undergo diagnostic thoracentesis to determine the nature of the effusion (ie, transudate, exudate) and to identify potential causes (eg, malignancy, infection).
There are two circumstances in which diagnostic thoracentesis is usually not required: when there is a small amount of pleural fluid and a secure clinical diagnosis (eg, viral pleurisy), or when there is clinically obvious heart failure (HF) without atypical features . Atypical features that should prompt consideration of diagnostic thoracentesis in a patient with HF include:
●Bilateral effusions that are of markedly disparate sizes